diff --git a/src/Grant/AbstractGrant.php b/src/Grant/AbstractGrant.php
index 49213331..45269ac7 100644
--- a/src/Grant/AbstractGrant.php
+++ b/src/Grant/AbstractGrant.php
@@ -472,16 +472,19 @@ abstract class AbstractGrant implements GrantTypeInterface
      * @throws OAuthServerException
      * @throws UniqueTokenIdentifierConstraintViolationException
      *
-     * @return RefreshTokenEntityInterface
+     * @return RefreshTokenEntityInterface|null
      */
     protected function issueRefreshToken(AccessTokenEntityInterface $accessToken)
     {
-        $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
-
         $refreshToken = $this->refreshTokenRepository->getNewRefreshToken();
+        if ($refreshToken === null) {
+            return null;
+        }
+
         $refreshToken->setExpiryDateTime((new DateTime())->add($this->refreshTokenTTL));
         $refreshToken->setAccessToken($accessToken);
 
+        $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
         while ($maxGenerationAttempts-- > 0) {
             $refreshToken->setIdentifier($this->generateUniqueIdentifier());
             try {
diff --git a/tests/Grant/AbstractGrantTest.php b/tests/Grant/AbstractGrantTest.php
index 6266df0a..1ed4a935 100644
--- a/tests/Grant/AbstractGrantTest.php
+++ b/tests/Grant/AbstractGrantTest.php
@@ -18,6 +18,7 @@ use LeagueTests\Stubs\AuthCodeEntity;
 use LeagueTests\Stubs\ClientEntity;
 use LeagueTests\Stubs\RefreshTokenEntity;
 use LeagueTests\Stubs\ScopeEntity;
+use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
 use Zend\Diactoros\ServerRequest;
 
@@ -346,6 +347,28 @@ class AbstractGrantTest extends TestCase
         $this->assertEquals($accessToken, $refreshToken->getAccessToken());
     }
 
+    public function testIssueNullRefreshToken()
+    {
+        /** @var RefreshTokenRepositoryInterface|MockObject $refreshTokenRepoMock */
+        $refreshTokenRepoMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
+        $refreshTokenRepoMock
+            ->expects($this->once())
+            ->method('getNewRefreshToken')
+            ->willReturn(null);
+
+        /** @var AbstractGrant $grantMock */
+        $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
+        $grantMock->setRefreshTokenTTL(new \DateInterval('PT1M'));
+        $grantMock->setRefreshTokenRepository($refreshTokenRepoMock);
+
+        $abstractGrantReflection = new \ReflectionClass($grantMock);
+        $issueRefreshTokenMethod = $abstractGrantReflection->getMethod('issueRefreshToken');
+        $issueRefreshTokenMethod->setAccessible(true);
+
+        $accessToken = new AccessTokenEntity();
+        $this->assertNull($issueRefreshTokenMethod->invoke($grantMock, $accessToken));
+    }
+
     public function testIssueAccessToken()
     {
         $accessTokenRepoMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();