diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0cb7da30..f74b4849 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - No longer need to enable PKCE with `enableCodeExchangeProof` flag. Any client sending a code challenge will initiate PKCE checks. (PR #938)
 - Function `getClientEntity()` no longer performs client validation (PR #938)
 - Password Grant now returns an invalid_grant error instead of invalid_credentials if a user cannot be validated (PR #967)
+- Use `DateTimeImmutable()` instead of `DateTime()`, `time()` instead of `(new DateTime())->getTimeStamp()`, and `DateTime::getTimeStamp()` instead of `DateTime::format('U')` (PR #963)
 
 ### Removed
 - `enableCodeExchangeProof` flag (PR #938)
diff --git a/src/AuthorizationServer.php b/src/AuthorizationServer.php
index f1e96146..81973b24 100644
--- a/src/AuthorizationServer.php
+++ b/src/AuthorizationServer.php
@@ -9,6 +9,7 @@
 
 namespace League\OAuth2\Server;
 
+use DateInterval;
 use Defuse\Crypto\Key;
 use League\Event\EmitterAwareInterface;
 use League\Event\EmitterAwareTrait;
@@ -34,7 +35,7 @@ class AuthorizationServer implements EmitterAwareInterface
     protected $enabledGrantTypes = [];
 
     /**
-     * @var \DateInterval[]
+     * @var DateInterval[]
      */
     protected $grantTypeAccessTokenTTL = [];
 
@@ -112,12 +113,12 @@ class AuthorizationServer implements EmitterAwareInterface
      * Enable a grant type on the server.
      *
      * @param GrantTypeInterface $grantType
-     * @param null|\DateInterval $accessTokenTTL
+     * @param null|DateInterval  $accessTokenTTL
      */
-    public function enableGrantType(GrantTypeInterface $grantType, \DateInterval $accessTokenTTL = null)
+    public function enableGrantType(GrantTypeInterface $grantType, DateInterval $accessTokenTTL = null)
     {
-        if ($accessTokenTTL instanceof \DateInterval === false) {
-            $accessTokenTTL = new \DateInterval('PT1H');
+        if ($accessTokenTTL === null) {
+            $accessTokenTTL = new DateInterval('PT1H');
         }
 
         $grantType->setAccessTokenRepository($this->accessTokenRepository);
diff --git a/src/Entities/RefreshTokenEntityInterface.php b/src/Entities/RefreshTokenEntityInterface.php
index e4f10400..551ad052 100644
--- a/src/Entities/RefreshTokenEntityInterface.php
+++ b/src/Entities/RefreshTokenEntityInterface.php
@@ -9,6 +9,8 @@
 
 namespace League\OAuth2\Server\Entities;
 
+use DateTimeImmutable;
+
 interface RefreshTokenEntityInterface
 {
     /**
@@ -28,16 +30,16 @@ interface RefreshTokenEntityInterface
     /**
      * Get the token's expiry date time.
      *
-     * @return \DateTime
+     * @return DateTimeImmutable
      */
     public function getExpiryDateTime();
 
     /**
      * Set the date time when the token expires.
      *
-     * @param \DateTime $dateTime
+     * @param DateTimeImmutable $dateTime
      */
-    public function setExpiryDateTime(\DateTime $dateTime);
+    public function setExpiryDateTime(DateTimeImmutable $dateTime);
 
     /**
      * Set the access token that the refresh token was associated with.
diff --git a/src/Entities/TokenInterface.php b/src/Entities/TokenInterface.php
index 378adbdc..7b063e13 100644
--- a/src/Entities/TokenInterface.php
+++ b/src/Entities/TokenInterface.php
@@ -9,6 +9,8 @@
 
 namespace League\OAuth2\Server\Entities;
 
+use DateTimeImmutable;
+
 interface TokenInterface
 {
     /**
@@ -28,16 +30,16 @@ interface TokenInterface
     /**
      * Get the token's expiry date time.
      *
-     * @return \DateTime
+     * @return DateTimeImmutable
      */
     public function getExpiryDateTime();
 
     /**
      * Set the date time when the token expires.
      *
-     * @param \DateTime $dateTime
+     * @param DateTimeImmutable $dateTime
      */
-    public function setExpiryDateTime(\DateTime $dateTime);
+    public function setExpiryDateTime(DateTimeImmutable $dateTime);
 
     /**
      * Set the identifier of the user associated with the token.
diff --git a/src/Entities/Traits/AccessTokenTrait.php b/src/Entities/Traits/AccessTokenTrait.php
index 501233e9..872e8c18 100644
--- a/src/Entities/Traits/AccessTokenTrait.php
+++ b/src/Entities/Traits/AccessTokenTrait.php
@@ -9,6 +9,7 @@
 
 namespace League\OAuth2\Server\Entities\Traits;
 
+use DateTimeImmutable;
 use Lcobucci\JWT\Builder;
 use Lcobucci\JWT\Signer\Key;
 use Lcobucci\JWT\Signer\Rsa\Sha256;
@@ -67,7 +68,7 @@ trait AccessTokenTrait
     abstract public function getClient();
 
     /**
-     * @return \DateTime
+     * @return DateTimeImmutable
      */
     abstract public function getExpiryDateTime();
 
diff --git a/src/Entities/Traits/RefreshTokenTrait.php b/src/Entities/Traits/RefreshTokenTrait.php
index fb9dbc68..f0f15444 100644
--- a/src/Entities/Traits/RefreshTokenTrait.php
+++ b/src/Entities/Traits/RefreshTokenTrait.php
@@ -9,6 +9,7 @@
 
 namespace League\OAuth2\Server\Entities\Traits;
 
+use DateTimeImmutable;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 
 trait RefreshTokenTrait
@@ -19,7 +20,7 @@ trait RefreshTokenTrait
     protected $accessToken;
 
     /**
-     * @var \DateTime
+     * @var DateTimeImmutable
      */
     protected $expiryDateTime;
 
@@ -42,7 +43,7 @@ trait RefreshTokenTrait
     /**
      * Get the token's expiry date time.
      *
-     * @return \DateTime
+     * @return DateTimeImmutable
      */
     public function getExpiryDateTime()
     {
@@ -52,9 +53,9 @@ trait RefreshTokenTrait
     /**
      * Set the date time when the token expires.
      *
-     * @param \DateTime $dateTime
+     * @param DateTimeImmutable $dateTime
      */
-    public function setExpiryDateTime(\DateTime $dateTime)
+    public function setExpiryDateTime(DateTimeImmutable $dateTime)
     {
         $this->expiryDateTime = $dateTime;
     }
diff --git a/src/Entities/Traits/TokenEntityTrait.php b/src/Entities/Traits/TokenEntityTrait.php
index c6653cce..5275c462 100644
--- a/src/Entities/Traits/TokenEntityTrait.php
+++ b/src/Entities/Traits/TokenEntityTrait.php
@@ -9,6 +9,7 @@
 
 namespace League\OAuth2\Server\Entities\Traits;
 
+use DateTimeImmutable;
 use League\OAuth2\Server\Entities\ClientEntityInterface;
 use League\OAuth2\Server\Entities\ScopeEntityInterface;
 
@@ -20,7 +21,7 @@ trait TokenEntityTrait
     protected $scopes = [];
 
     /**
-     * @var \DateTime
+     * @var DateTimeImmutable
      */
     protected $expiryDateTime;
 
@@ -57,7 +58,7 @@ trait TokenEntityTrait
     /**
      * Get the token's expiry date time.
      *
-     * @return \DateTime
+     * @return DateTimeImmutable
      */
     public function getExpiryDateTime()
     {
@@ -67,9 +68,9 @@ trait TokenEntityTrait
     /**
      * Set the date time when the token expires.
      *
-     * @param \DateTime $dateTime
+     * @param DateTimeImmutable $dateTime
      */
-    public function setExpiryDateTime(\DateTime $dateTime)
+    public function setExpiryDateTime(DateTimeImmutable $dateTime)
     {
         $this->expiryDateTime = $dateTime;
     }
diff --git a/src/Grant/AbstractGrant.php b/src/Grant/AbstractGrant.php
index 65ab16cf..d64c9697 100644
--- a/src/Grant/AbstractGrant.php
+++ b/src/Grant/AbstractGrant.php
@@ -10,6 +10,8 @@
  */
 namespace League\OAuth2\Server\Grant;
 
+use DateInterval;
+use DateTimeImmutable;
 use League\Event\EmitterAwareTrait;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\CryptTrait;
@@ -72,7 +74,7 @@ abstract class AbstractGrant implements GrantTypeInterface
     protected $userRepository;
 
     /**
-     * @var \DateInterval
+     * @var DateInterval
      */
     protected $refreshTokenTTL;
 
@@ -137,7 +139,7 @@ abstract class AbstractGrant implements GrantTypeInterface
     /**
      * {@inheritdoc}
      */
-    public function setRefreshTokenTTL(\DateInterval $refreshTokenTTL)
+    public function setRefreshTokenTTL(DateInterval $refreshTokenTTL)
     {
         $this->refreshTokenTTL = $refreshTokenTTL;
     }
@@ -367,7 +369,7 @@ abstract class AbstractGrant implements GrantTypeInterface
     /**
      * Issue an access token.
      *
-     * @param \DateInterval          $accessTokenTTL
+     * @param DateInterval           $accessTokenTTL
      * @param ClientEntityInterface  $client
      * @param string|null            $userIdentifier
      * @param ScopeEntityInterface[] $scopes
@@ -378,7 +380,7 @@ abstract class AbstractGrant implements GrantTypeInterface
      * @return AccessTokenEntityInterface
      */
     protected function issueAccessToken(
-        \DateInterval $accessTokenTTL,
+        DateInterval $accessTokenTTL,
         ClientEntityInterface $client,
         $userIdentifier,
         array $scopes = []
@@ -386,7 +388,7 @@ abstract class AbstractGrant implements GrantTypeInterface
         $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
 
         $accessToken = $this->accessTokenRepository->getNewToken($client, $scopes, $userIdentifier);
-        $accessToken->setExpiryDateTime((new \DateTime())->add($accessTokenTTL));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add($accessTokenTTL));
         $accessToken->setPrivateKey($this->privateKey);
 
         while ($maxGenerationAttempts-- > 0) {
@@ -406,7 +408,7 @@ abstract class AbstractGrant implements GrantTypeInterface
     /**
      * Issue an auth code.
      *
-     * @param \DateInterval          $authCodeTTL
+     * @param DateInterval           $authCodeTTL
      * @param ClientEntityInterface  $client
      * @param string                 $userIdentifier
      * @param string|null            $redirectUri
@@ -418,7 +420,7 @@ abstract class AbstractGrant implements GrantTypeInterface
      * @return AuthCodeEntityInterface
      */
     protected function issueAuthCode(
-        \DateInterval $authCodeTTL,
+        DateInterval $authCodeTTL,
         ClientEntityInterface $client,
         $userIdentifier,
         $redirectUri,
@@ -427,7 +429,7 @@ abstract class AbstractGrant implements GrantTypeInterface
         $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
 
         $authCode = $this->authCodeRepository->getNewAuthCode();
-        $authCode->setExpiryDateTime((new \DateTime())->add($authCodeTTL));
+        $authCode->setExpiryDateTime((new DateTimeImmutable())->add($authCodeTTL));
         $authCode->setClient($client);
         $authCode->setUserIdentifier($userIdentifier);
 
@@ -466,7 +468,7 @@ abstract class AbstractGrant implements GrantTypeInterface
         $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
 
         $refreshToken = $this->refreshTokenRepository->getNewRefreshToken();
-        $refreshToken->setExpiryDateTime((new \DateTime())->add($this->refreshTokenTTL));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add($this->refreshTokenTTL));
         $refreshToken->setAccessToken($accessToken);
 
         while ($maxGenerationAttempts-- > 0) {
diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index c340fe96..a26ea6ec 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -9,6 +9,8 @@
 
 namespace League\OAuth2\Server\Grant;
 
+use DateInterval;
+use DateTimeImmutable;
 use League\OAuth2\Server\CodeChallengeVerifiers\CodeChallengeVerifierInterface;
 use League\OAuth2\Server\CodeChallengeVerifiers\PlainVerifier;
 use League\OAuth2\Server\CodeChallengeVerifiers\S256Verifier;
@@ -27,7 +29,7 @@ use Psr\Http\Message\ServerRequestInterface;
 class AuthCodeGrant extends AbstractAuthorizeGrant
 {
     /**
-     * @var \DateInterval
+     * @var DateInterval
      */
     private $authCodeTTL;
 
@@ -44,17 +46,17 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
     /**
      * @param AuthCodeRepositoryInterface     $authCodeRepository
      * @param RefreshTokenRepositoryInterface $refreshTokenRepository
-     * @param \DateInterval                   $authCodeTTL
+     * @param DateInterval                    $authCodeTTL
      */
     public function __construct(
         AuthCodeRepositoryInterface $authCodeRepository,
         RefreshTokenRepositoryInterface $refreshTokenRepository,
-        \DateInterval $authCodeTTL
+        DateInterval $authCodeTTL
     ) {
         $this->setAuthCodeRepository($authCodeRepository);
         $this->setRefreshTokenRepository($refreshTokenRepository);
         $this->authCodeTTL = $authCodeTTL;
-        $this->refreshTokenTTL = new \DateInterval('P1M');
+        $this->refreshTokenTTL = new DateInterval('P1M');
 
         // SHOULD ONLY DO THIS IS SHA256 is supported
         $s256Verifier = new S256Verifier();
@@ -79,7 +81,7 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
      *
      * @param ServerRequestInterface $request
      * @param ResponseTypeInterface  $responseType
-     * @param \DateInterval          $accessTokenTTL
+     * @param DateInterval           $accessTokenTTL
      *
      * @throws OAuthServerException
      *
@@ -88,7 +90,7 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
     public function respondToAccessTokenRequest(
         ServerRequestInterface $request,
         ResponseTypeInterface $responseType,
-        \DateInterval $accessTokenTTL
+        DateInterval $accessTokenTTL
     ) {
         list($clientId) = $this->getClientCredentials($request);
 
@@ -350,7 +352,7 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
                 'auth_code_id'          => $authCode->getIdentifier(),
                 'scopes'                => $authCode->getScopes(),
                 'user_id'               => $authCode->getUserIdentifier(),
-                'expire_time'           => (new \DateTime())->add($this->authCodeTTL)->format('U'),
+                'expire_time'           => (new DateTimeImmutable())->add($this->authCodeTTL)->getTimestamp(),
                 'code_challenge'        => $authorizationRequest->getCodeChallenge(),
                 'code_challenge_method' => $authorizationRequest->getCodeChallengeMethod(),
             ];
@@ -360,11 +362,7 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
                 $this->makeRedirectUri(
                     $finalRedirectUri,
                     [
-                        'code'  => $this->encrypt(
-                            json_encode(
-                                $payload
-                            )
-                        ),
+                        'code'  => $this->encrypt(json_encode($payload)),
                         'state' => $authorizationRequest->getState(),
                     ]
                 )
diff --git a/src/Grant/ClientCredentialsGrant.php b/src/Grant/ClientCredentialsGrant.php
index 026ce5e5..9f647965 100644
--- a/src/Grant/ClientCredentialsGrant.php
+++ b/src/Grant/ClientCredentialsGrant.php
@@ -11,6 +11,7 @@
 
 namespace League\OAuth2\Server\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\RequestEvent;
 use League\OAuth2\Server\ResponseTypes\ResponseTypeInterface;
 use Psr\Http\Message\ServerRequestInterface;
@@ -26,7 +27,7 @@ class ClientCredentialsGrant extends AbstractGrant
     public function respondToAccessTokenRequest(
         ServerRequestInterface $request,
         ResponseTypeInterface $responseType,
-        \DateInterval $accessTokenTTL
+        DateInterval $accessTokenTTL
     ) {
         // Validate request
         $client = $this->validateClient($request);
diff --git a/src/Grant/GrantTypeInterface.php b/src/Grant/GrantTypeInterface.php
index 2aee367f..41ebeb5f 100644
--- a/src/Grant/GrantTypeInterface.php
+++ b/src/Grant/GrantTypeInterface.php
@@ -11,6 +11,7 @@
 
 namespace League\OAuth2\Server\Grant;
 
+use DateInterval;
 use Defuse\Crypto\Key;
 use League\Event\EmitterAwareInterface;
 use League\OAuth2\Server\CryptKey;
@@ -29,9 +30,9 @@ interface GrantTypeInterface extends EmitterAwareInterface
     /**
      * Set refresh token TTL.
      *
-     * @param \DateInterval $refreshTokenTTL
+     * @param DateInterval $refreshTokenTTL
      */
-    public function setRefreshTokenTTL(\DateInterval $refreshTokenTTL);
+    public function setRefreshTokenTTL(DateInterval $refreshTokenTTL);
 
     /**
      * Return the grant identifier that can be used in matching up requests.
@@ -45,14 +46,14 @@ interface GrantTypeInterface extends EmitterAwareInterface
      *
      * @param ServerRequestInterface $request
      * @param ResponseTypeInterface  $responseType
-     * @param \DateInterval          $accessTokenTTL
+     * @param DateInterval           $accessTokenTTL
      *
      * @return ResponseTypeInterface
      */
     public function respondToAccessTokenRequest(
         ServerRequestInterface $request,
         ResponseTypeInterface $responseType,
-        \DateInterval $accessTokenTTL
+        DateInterval $accessTokenTTL
     );
 
     /**
diff --git a/src/Grant/ImplicitGrant.php b/src/Grant/ImplicitGrant.php
index 6a71ab08..5fc08cf1 100644
--- a/src/Grant/ImplicitGrant.php
+++ b/src/Grant/ImplicitGrant.php
@@ -9,6 +9,7 @@
 
 namespace League\OAuth2\Server\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\Entities\ClientEntityInterface;
 use League\OAuth2\Server\Entities\UserEntityInterface;
 use League\OAuth2\Server\Exception\OAuthServerException;
@@ -22,7 +23,7 @@ use Psr\Http\Message\ServerRequestInterface;
 class ImplicitGrant extends AbstractAuthorizeGrant
 {
     /**
-     * @var \DateInterval
+     * @var DateInterval
      */
     private $accessTokenTTL;
 
@@ -32,21 +33,21 @@ class ImplicitGrant extends AbstractAuthorizeGrant
     private $queryDelimiter;
 
     /**
-     * @param \DateInterval $accessTokenTTL
-     * @param string        $queryDelimiter
+     * @param DateInterval $accessTokenTTL
+     * @param string       $queryDelimiter
      */
-    public function __construct(\DateInterval $accessTokenTTL, $queryDelimiter = '#')
+    public function __construct(DateInterval $accessTokenTTL, $queryDelimiter = '#')
     {
         $this->accessTokenTTL = $accessTokenTTL;
         $this->queryDelimiter = $queryDelimiter;
     }
 
     /**
-     * @param \DateInterval $refreshTokenTTL
+     * @param DateInterval $refreshTokenTTL
      *
      * @throw \LogicException
      */
-    public function setRefreshTokenTTL(\DateInterval $refreshTokenTTL)
+    public function setRefreshTokenTTL(DateInterval $refreshTokenTTL)
     {
         throw new \LogicException('The Implicit Grant does not return refresh tokens');
     }
@@ -84,14 +85,14 @@ class ImplicitGrant extends AbstractAuthorizeGrant
      *
      * @param ServerRequestInterface $request
      * @param ResponseTypeInterface  $responseType
-     * @param \DateInterval          $accessTokenTTL
+     * @param DateInterval           $accessTokenTTL
      *
      * @return ResponseTypeInterface
      */
     public function respondToAccessTokenRequest(
         ServerRequestInterface $request,
         ResponseTypeInterface $responseType,
-        \DateInterval $accessTokenTTL
+        DateInterval $accessTokenTTL
     ) {
         throw new \LogicException('This grant does not used this method');
     }
@@ -203,7 +204,7 @@ class ImplicitGrant extends AbstractAuthorizeGrant
                     [
                         'access_token' => (string) $accessToken,
                         'token_type'   => 'Bearer',
-                        'expires_in'   => $accessToken->getExpiryDateTime()->getTimestamp() - (new \DateTime())->getTimestamp(),
+                        'expires_in'   => $accessToken->getExpiryDateTime()->getTimestamp() - \time(),
                         'state'        => $authorizationRequest->getState(),
                     ],
                     $this->queryDelimiter
diff --git a/src/Grant/PasswordGrant.php b/src/Grant/PasswordGrant.php
index 412ac117..7375d436 100644
--- a/src/Grant/PasswordGrant.php
+++ b/src/Grant/PasswordGrant.php
@@ -11,6 +11,7 @@
 
 namespace League\OAuth2\Server\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\Entities\ClientEntityInterface;
 use League\OAuth2\Server\Entities\UserEntityInterface;
 use League\OAuth2\Server\Exception\OAuthServerException;
@@ -36,7 +37,7 @@ class PasswordGrant extends AbstractGrant
         $this->setUserRepository($userRepository);
         $this->setRefreshTokenRepository($refreshTokenRepository);
 
-        $this->refreshTokenTTL = new \DateInterval('P1M');
+        $this->refreshTokenTTL = new DateInterval('P1M');
     }
 
     /**
@@ -45,7 +46,7 @@ class PasswordGrant extends AbstractGrant
     public function respondToAccessTokenRequest(
         ServerRequestInterface $request,
         ResponseTypeInterface $responseType,
-        \DateInterval $accessTokenTTL
+        DateInterval $accessTokenTTL
     ) {
         // Validate request
         $client = $this->validateClient($request);
diff --git a/src/Grant/RefreshTokenGrant.php b/src/Grant/RefreshTokenGrant.php
index 519954be..cde4beee 100644
--- a/src/Grant/RefreshTokenGrant.php
+++ b/src/Grant/RefreshTokenGrant.php
@@ -11,6 +11,7 @@
 
 namespace League\OAuth2\Server\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\Exception\OAuthServerException;
 use League\OAuth2\Server\Repositories\RefreshTokenRepositoryInterface;
 use League\OAuth2\Server\RequestEvent;
@@ -29,7 +30,7 @@ class RefreshTokenGrant extends AbstractGrant
     {
         $this->setRefreshTokenRepository($refreshTokenRepository);
 
-        $this->refreshTokenTTL = new \DateInterval('P1M');
+        $this->refreshTokenTTL = new DateInterval('P1M');
     }
 
     /**
@@ -38,7 +39,7 @@ class RefreshTokenGrant extends AbstractGrant
     public function respondToAccessTokenRequest(
         ServerRequestInterface $request,
         ResponseTypeInterface $responseType,
-        \DateInterval $accessTokenTTL
+        DateInterval $accessTokenTTL
     ) {
         // Validate request
         $client = $this->validateClient($request);
diff --git a/src/ResponseTypes/BearerTokenResponse.php b/src/ResponseTypes/BearerTokenResponse.php
index 2e658215..ddcadd63 100644
--- a/src/ResponseTypes/BearerTokenResponse.php
+++ b/src/ResponseTypes/BearerTokenResponse.php
@@ -26,7 +26,7 @@ class BearerTokenResponse extends AbstractResponseType
 
         $responseParams = [
             'token_type'   => 'Bearer',
-            'expires_in'   => $expireDateTime - (new \DateTime())->getTimestamp(),
+            'expires_in'   => $expireDateTime - \time(),
             'access_token' => (string) $this->accessToken,
         ];
 
diff --git a/tests/AuthorizationServerTest.php b/tests/AuthorizationServerTest.php
index 7e83ee5e..9fe1a020 100644
--- a/tests/AuthorizationServerTest.php
+++ b/tests/AuthorizationServerTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests;
 
+use DateInterval;
 use League\OAuth2\Server\AuthorizationServer;
 use League\OAuth2\Server\Exception\OAuthServerException;
 use League\OAuth2\Server\Grant\AuthCodeGrant;
@@ -48,7 +49,7 @@ class AuthorizationServerTest extends TestCase
             new StubResponseType()
         );
 
-        $server->enableGrantType(new ClientCredentialsGrant(), new \DateInterval('PT1M'));
+        $server->enableGrantType(new ClientCredentialsGrant(), new DateInterval('PT1M'));
 
         try {
             $server->respondToAccessTokenRequest(ServerRequestFactory::fromGlobals(), new Response);
@@ -81,7 +82,7 @@ class AuthorizationServerTest extends TestCase
         );
 
         $server->setDefaultScope(self::DEFAULT_SCOPE);
-        $server->enableGrantType(new ClientCredentialsGrant(), new \DateInterval('PT1M'));
+        $server->enableGrantType(new ClientCredentialsGrant(), new DateInterval('PT1M'));
 
         $_POST['grant_type'] = 'client_credentials';
         $_POST['client_id'] = 'foo';
@@ -127,7 +128,7 @@ class AuthorizationServerTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $server->enableGrantType($grant);
@@ -159,7 +160,7 @@ class AuthorizationServerTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
@@ -200,7 +201,7 @@ class AuthorizationServerTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
diff --git a/tests/Grant/AbstractGrantTest.php b/tests/Grant/AbstractGrantTest.php
index d6ddd4b1..33103130 100644
--- a/tests/Grant/AbstractGrantTest.php
+++ b/tests/Grant/AbstractGrantTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\AuthCodeEntityInterface;
@@ -325,7 +326,7 @@ class AbstractGrantTest extends TestCase
 
         /** @var AbstractGrant $grantMock */
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
-        $grantMock->setRefreshTokenTTL(new \DateInterval('PT1M'));
+        $grantMock->setRefreshTokenTTL(new DateInterval('PT1M'));
         $grantMock->setRefreshTokenRepository($refreshTokenRepoMock);
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
@@ -356,7 +357,7 @@ class AbstractGrantTest extends TestCase
         /** @var AccessTokenEntityInterface $accessToken */
         $accessToken = $issueAccessTokenMethod->invoke(
             $grantMock,
-            new \DateInterval('PT1H'),
+            new DateInterval('PT1H'),
             new ClientEntity(),
             123,
             [new ScopeEntity()]
@@ -381,7 +382,7 @@ class AbstractGrantTest extends TestCase
             AuthCodeEntityInterface::class,
             $issueAuthCodeMethod->invoke(
                 $grantMock,
-                new \DateInterval('PT1H'),
+                new DateInterval('PT1H'),
                 new ClientEntity(),
                 123,
                 'http://foo/bar',
diff --git a/tests/Grant/AuthCodeGrantTest.php b/tests/Grant/AuthCodeGrantTest.php
index c7f08a1a..9b6f24d1 100644
--- a/tests/Grant/AuthCodeGrantTest.php
+++ b/tests/Grant/AuthCodeGrantTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\RefreshTokenEntityInterface;
@@ -49,7 +50,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $this->assertEquals('authorization_code', $grant->getIdentifier());
@@ -60,7 +61,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $request = new ServerRequest(
@@ -96,7 +97,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
@@ -135,7 +136,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
@@ -173,7 +174,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -212,7 +213,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -249,7 +250,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -286,7 +287,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -321,7 +322,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
@@ -353,7 +354,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
@@ -388,7 +389,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
@@ -424,7 +425,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
@@ -464,7 +465,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -505,7 +506,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setEncryptionKey($this->cryptStub->getKey());
 
@@ -530,7 +531,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setEncryptionKey($this->cryptStub->getKey());
 
@@ -562,7 +563,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
@@ -600,7 +601,7 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
@@ -695,7 +696,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
@@ -733,7 +734,7 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
@@ -764,7 +765,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -806,7 +807,7 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
@@ -837,7 +838,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -879,7 +880,7 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
@@ -900,7 +901,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
@@ -930,7 +931,7 @@ class AuthCodeGrantTest extends TestCase
             ]
         );
 
-        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
     }
 
     /**
@@ -948,7 +949,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
@@ -979,7 +980,7 @@ class AuthCodeGrantTest extends TestCase
             ]
         );
 
-        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
     }
 
     /**
@@ -1000,7 +1001,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
@@ -1025,7 +1026,7 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /* @var StubResponseType $response */
-        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
     }
 
     public function testRespondToAccessTokenRequestExpiredCode()
@@ -1036,7 +1037,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -1072,7 +1073,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Authorization code has expired');
         }
@@ -1099,7 +1100,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepositoryMock,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
@@ -1136,7 +1137,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Authorization code has been revoked');
         }
@@ -1160,7 +1161,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
@@ -1197,7 +1198,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Authorization code was not issued to this client');
         }
@@ -1221,7 +1222,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
@@ -1247,7 +1248,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Cannot decrypt the authorization code');
         }
@@ -1278,7 +1279,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -1320,7 +1321,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Failed to verify `code_verifier`.');
         }
@@ -1351,7 +1352,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -1393,7 +1394,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Code Verifier must follow the specifications of RFC-7636.');
         }
@@ -1424,7 +1425,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -1466,7 +1467,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Code Verifier must follow the specifications of RFC-7636.');
         }
@@ -1497,7 +1498,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -1539,7 +1540,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Code Verifier must follow the specifications of RFC-7636.');
         }
@@ -1570,7 +1571,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
@@ -1611,7 +1612,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Check the `code_verifier` parameter');
         }
@@ -1634,7 +1635,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setEncryptionKey($this->cryptStub->getKey());
         $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
@@ -1661,7 +1662,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setEncryptionKey($this->cryptStub->getKey());
 
@@ -1687,7 +1688,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $this->assertInstanceOf(RedirectResponse::class, $grant->completeAuthorizationRequest($authRequest));
@@ -1718,7 +1719,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
@@ -1756,7 +1757,7 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
@@ -1790,7 +1791,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
@@ -1828,7 +1829,7 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
@@ -1862,7 +1863,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
@@ -1900,7 +1901,7 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
@@ -1914,7 +1915,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->completeAuthorizationRequest(new AuthorizationRequest());
@@ -1935,7 +1936,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $grant->setClientRepository($clientRepositoryMock);
diff --git a/tests/Grant/ClientCredentialsGrantTest.php b/tests/Grant/ClientCredentialsGrantTest.php
index dfd78b41..b02f1190 100644
--- a/tests/Grant/ClientCredentialsGrantTest.php
+++ b/tests/Grant/ClientCredentialsGrantTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Grant\ClientCredentialsGrant;
@@ -56,7 +57,7 @@ class ClientCredentialsGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $responseType->getAccessToken());
     }
diff --git a/tests/Grant/ImplicitGrantTest.php b/tests/Grant/ImplicitGrantTest.php
index df7b6985..5e702e01 100644
--- a/tests/Grant/ImplicitGrantTest.php
+++ b/tests/Grant/ImplicitGrantTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Exception\OAuthServerException;
 use League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException;
@@ -37,13 +38,13 @@ class ImplicitGrantTest extends TestCase
 
     public function testGetIdentifier()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $this->assertEquals('implicit', $grant->getIdentifier());
     }
 
     public function testCanRespondToAccessTokenRequest()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
 
         $this->assertFalse(
             $grant->canRespondToAccessTokenRequest(new ServerRequest())
@@ -55,17 +56,17 @@ class ImplicitGrantTest extends TestCase
      */
     public function testRespondToAccessTokenRequest()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->respondToAccessTokenRequest(
             new ServerRequest(),
             new StubResponseType(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
     }
 
     public function testCanRespondToAuthorizationRequest()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
 
         $request = new ServerRequest(
             [],
@@ -96,7 +97,7 @@ class ImplicitGrantTest extends TestCase
         $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scopeEntity);
         $scopeRepositoryMock->method('finalizeScopes')->willReturnArgument(0);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setDefaultScope(self::DEFAULT_SCOPE);
@@ -131,7 +132,7 @@ class ImplicitGrantTest extends TestCase
         $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scopeEntity);
         $scopeRepositoryMock->method('finalizeScopes')->willReturnArgument(0);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setDefaultScope(self::DEFAULT_SCOPE);
@@ -162,7 +163,7 @@ class ImplicitGrantTest extends TestCase
     {
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
 
         $request = new ServerRequest(
@@ -190,7 +191,7 @@ class ImplicitGrantTest extends TestCase
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn(null);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
 
         $request = new ServerRequest(
@@ -221,7 +222,7 @@ class ImplicitGrantTest extends TestCase
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
 
         $request = new ServerRequest(
@@ -253,7 +254,7 @@ class ImplicitGrantTest extends TestCase
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
 
         $request = new ServerRequest(
@@ -292,7 +293,7 @@ class ImplicitGrantTest extends TestCase
         $accessTokenRepositoryMock->method('getNewToken')->willReturn($accessToken);
         $accessTokenRepositoryMock->method('persistNewAccessToken')->willReturnSelf();
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
 
@@ -315,7 +316,7 @@ class ImplicitGrantTest extends TestCase
         $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
         $accessTokenRepositoryMock->method('persistNewAccessToken')->willReturnSelf();
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
 
@@ -342,7 +343,7 @@ class ImplicitGrantTest extends TestCase
         $accessTokenRepositoryMock->expects($this->at(0))->method('persistNewAccessToken')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
         $accessTokenRepositoryMock->expects($this->at(1))->method('persistNewAccessToken')->willReturnSelf();
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
 
@@ -366,7 +367,7 @@ class ImplicitGrantTest extends TestCase
         $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
         $accessTokenRepositoryMock->method('persistNewAccessToken')->willThrowException(OAuthServerException::serverError('something bad happened'));
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
 
@@ -390,7 +391,7 @@ class ImplicitGrantTest extends TestCase
         $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
         $accessTokenRepositoryMock->method('persistNewAccessToken')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
 
@@ -402,8 +403,8 @@ class ImplicitGrantTest extends TestCase
      */
     public function testSetRefreshTokenTTL()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
-        $grant->setRefreshTokenTTL(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
+        $grant->setRefreshTokenTTL(new DateInterval('PT10M'));
     }
 
     /**
@@ -411,7 +412,7 @@ class ImplicitGrantTest extends TestCase
      */
     public function testSetRefreshTokenRepository()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $refreshTokenRepositoryMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
     }
@@ -421,7 +422,7 @@ class ImplicitGrantTest extends TestCase
      */
     public function testCompleteAuthorizationRequestNoUser()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->completeAuthorizationRequest(new AuthorizationRequest());
     }
 }
diff --git a/tests/Grant/PasswordGrantTest.php b/tests/Grant/PasswordGrantTest.php
index 378fee6f..88592339 100644
--- a/tests/Grant/PasswordGrantTest.php
+++ b/tests/Grant/PasswordGrantTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\RefreshTokenEntityInterface;
@@ -74,7 +75,7 @@ class PasswordGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $responseType->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $responseType->getRefreshToken());
@@ -108,7 +109,7 @@ class PasswordGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
     /**
@@ -140,7 +141,7 @@ class PasswordGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
     /**
@@ -175,6 +176,6 @@ class PasswordGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 }
diff --git a/tests/Grant/RefreshTokenGrantTest.php b/tests/Grant/RefreshTokenGrantTest.php
index 89598115..6d1cbdf2 100644
--- a/tests/Grant/RefreshTokenGrantTest.php
+++ b/tests/Grant/RefreshTokenGrantTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\RefreshTokenEntityInterface;
@@ -88,7 +89,7 @@ class RefreshTokenGrantTest extends TestCase
         ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $responseType->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $responseType->getRefreshToken());
@@ -145,7 +146,7 @@ class RefreshTokenGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $responseType->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $responseType->getRefreshToken());
@@ -204,7 +205,7 @@ class RefreshTokenGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
     /**
@@ -236,7 +237,7 @@ class RefreshTokenGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
     /**
@@ -271,7 +272,7 @@ class RefreshTokenGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
     /**
@@ -320,7 +321,7 @@ class RefreshTokenGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
     /**
@@ -366,7 +367,7 @@ class RefreshTokenGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
     /**
@@ -413,6 +414,6 @@ class RefreshTokenGrantTest extends TestCase
         );
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 }
diff --git a/tests/Middleware/AuthorizationServerMiddlewareTest.php b/tests/Middleware/AuthorizationServerMiddlewareTest.php
index dcfcfbd9..a7ef803d 100644
--- a/tests/Middleware/AuthorizationServerMiddlewareTest.php
+++ b/tests/Middleware/AuthorizationServerMiddlewareTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Middleware;
 
+use DateInterval;
 use League\OAuth2\Server\AuthorizationServer;
 use League\OAuth2\Server\Exception\OAuthServerException;
 use League\OAuth2\Server\Grant\ClientCredentialsGrant;
@@ -77,7 +78,7 @@ class AuthorizationServerMiddlewareTest extends TestCase
             new StubResponseType()
         );
 
-        $server->enableGrantType(new ClientCredentialsGrant(), new \DateInterval('PT1M'));
+        $server->enableGrantType(new ClientCredentialsGrant(), new DateInterval('PT1M'));
 
         $_POST['grant_type'] = 'client_credentials';
         $_POST['client_id'] = 'foo';
diff --git a/tests/Middleware/ResourceServerMiddlewareTest.php b/tests/Middleware/ResourceServerMiddlewareTest.php
index d1a96042..7210567b 100644
--- a/tests/Middleware/ResourceServerMiddlewareTest.php
+++ b/tests/Middleware/ResourceServerMiddlewareTest.php
@@ -2,6 +2,8 @@
 
 namespace LeagueTests\Middleware;
 
+use DateInterval;
+use DateTimeImmutable;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Middleware\ResourceServerMiddleware;
 use League\OAuth2\Server\Repositories\AccessTokenRepositoryInterface;
@@ -27,7 +29,7 @@ class ResourceServerMiddlewareTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('test');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
         $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
@@ -63,7 +65,7 @@ class ResourceServerMiddlewareTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('test');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->sub(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->sub(new DateInterval('PT1H')));
         $accessToken->setClient($client);
         $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
diff --git a/tests/ResponseTypes/BearerResponseTypeTest.php b/tests/ResponseTypes/BearerResponseTypeTest.php
index 2eb87238..5eddfdef 100644
--- a/tests/ResponseTypes/BearerResponseTypeTest.php
+++ b/tests/ResponseTypes/BearerResponseTypeTest.php
@@ -2,6 +2,8 @@
 
 namespace LeagueTests\ResponseTypes;
 
+use DateInterval;
+use DateTimeImmutable;
 use League\OAuth2\Server\AuthorizationValidators\BearerTokenValidator;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Exception\OAuthServerException;
@@ -32,7 +34,7 @@ class BearerResponseTypeTest extends TestCase
 
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
         $accessToken->addScope($scope);
         $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
@@ -40,7 +42,7 @@ class BearerResponseTypeTest extends TestCase
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);
@@ -75,7 +77,7 @@ class BearerResponseTypeTest extends TestCase
 
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
         $accessToken->addScope($scope);
         $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
@@ -83,7 +85,7 @@ class BearerResponseTypeTest extends TestCase
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);
@@ -119,14 +121,14 @@ class BearerResponseTypeTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
         $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);
@@ -165,14 +167,14 @@ class BearerResponseTypeTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
         $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);
@@ -208,14 +210,14 @@ class BearerResponseTypeTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
         $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);