diff --git a/src/AuthorizationServer.php b/src/AuthorizationServer.php
index 805d1e73..1122749b 100644
--- a/src/AuthorizationServer.php
+++ b/src/AuthorizationServer.php
@@ -73,7 +73,7 @@ class AuthorizationServer implements EmitterAwareInterface
     /**
      * @var string
      */
-    private $defaultScope = null;
+    private $defaultScope = '';
 
     /**
      * New server instance.
@@ -209,4 +209,14 @@ class AuthorizationServer implements EmitterAwareInterface
 
         return $this->responseType;
     }
+
+    /**
+     * Set the default scope for the authorization server.
+     *
+     * @param string $defaultScope
+     */
+    public function setDefaultScope($defaultScope)
+    {
+        $this->defaultScope = $defaultScope;
+    }
 }
diff --git a/tests/AuthorizationServerTest.php b/tests/AuthorizationServerTest.php
index 15376c22..594a7ca6 100644
--- a/tests/AuthorizationServerTest.php
+++ b/tests/AuthorizationServerTest.php
@@ -45,7 +45,6 @@ class AuthorizationServerTest extends \PHPUnit_Framework_TestCase
             $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock(),
             'file://' . __DIR__ . '/Stubs/private.key',
             base64_encode(random_bytes(36)),
-            self::DEFAULT_SCOPE,
             new StubResponseType()
         );
 
@@ -78,10 +77,10 @@ class AuthorizationServerTest extends \PHPUnit_Framework_TestCase
             $scopeRepositoryMock,
             'file://' . __DIR__ . '/Stubs/private.key',
             base64_encode(random_bytes(36)),
-            self::DEFAULT_SCOPE,
             new StubResponseType()
         );
 
+        $server->setDefaultScope(self::DEFAULT_SCOPE);
         $server->enableGrantType(new ClientCredentialsGrant(), new \DateInterval('PT1M'));
 
         $_POST['grant_type'] = 'client_credentials';
@@ -166,9 +165,10 @@ class AuthorizationServerTest extends \PHPUnit_Framework_TestCase
             $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock(),
             $scopeRepositoryMock,
             'file://' . __DIR__ . '/Stubs/private.key',
-            'file://' . __DIR__ . '/Stubs/public.key',
-            self::DEFAULT_SCOPE
+            'file://' . __DIR__ . '/Stubs/public.key'
         );
+
+        $server->setDefaultScope(self::DEFAULT_SCOPE);
         $server->enableGrantType($grant);
 
         $request = new ServerRequest(
diff --git a/tests/Middleware/AuthorizationServerMiddlewareTest.php b/tests/Middleware/AuthorizationServerMiddlewareTest.php
index b41774de..1556405a 100644
--- a/tests/Middleware/AuthorizationServerMiddlewareTest.php
+++ b/tests/Middleware/AuthorizationServerMiddlewareTest.php
@@ -40,10 +40,10 @@ class AuthorizationServerMiddlewareTest extends \PHPUnit_Framework_TestCase
             $scopeRepositoryMock,
             'file://' . __DIR__ . '/../Stubs/private.key',
             base64_encode(random_bytes(36)),
-            self::DEFAULT_SCOPE,
             new StubResponseType()
         );
 
+        $server->setDefaultScope(self::DEFAULT_SCOPE);
         $server->enableGrantType(new ClientCredentialsGrant());
 
         $_POST['grant_type'] = 'client_credentials';