diff --git a/Storage/OAuthStorage.php b/Storage/OAuthStorage.php
index bb0bc86b..dd17c897 100644
--- a/Storage/OAuthStorage.php
+++ b/Storage/OAuthStorage.php
@@ -236,7 +236,7 @@ public function unsetRefreshToken($tokenString)
     /**
      * {@inheritdoc}
      */
-    public function checkGrantExtension(IOAuth2Client $client, $uri, array $inputData, array $authHeaders): array|bool
+    public function checkGrantExtension(IOAuth2Client $client, $uri, array $inputData, array $authHeaders): bool|array
     {
         if (!isset($this->grantExtensions[$uri])) {
             throw new OAuth2ServerException(Response::HTTP_BAD_REQUEST, OAuth2::ERROR_UNSUPPORTED_GRANT_TYPE);
diff --git a/Tests/Storage/OAuthStorageTest.php b/Tests/Storage/OAuthStorageTest.php
index 345cbd8e..c6891bc6 100644
--- a/Tests/Storage/OAuthStorageTest.php
+++ b/Tests/Storage/OAuthStorageTest.php
@@ -539,6 +539,28 @@ public function testValidGrantExtensionWithData(): void
         );
     }
 
+    public function testValidGrantExtensionWithData(): void
+    {
+        $grantExtension = $this->getMockBuilder('FOS\OAuthServerBundle\Storage\GrantExtensionInterface')
+            ->disableOriginalConstructor()
+            ->getMock()
+        ;
+        $grantExtensionData = ['data' => 'Foo'];
+        $grantExtension
+            ->expects($this->once())
+            ->method('checkGrantExtension')
+            ->will($this->returnValue($grantExtensionData))
+        ;
+        $this->storage->setGrantExtension('https://friendsofsymfony.com/grants/foo', $grantExtension);
+        $client = $this->getMockBuilder('OAuth2\Model\IOAuth2Client')
+            ->disableOriginalConstructor()
+            ->getMock()
+        ;
+        $this->assertEquals(
+            $grantExtensionData,
+            $this->storage->checkGrantExtension($client, 'https://friendsofsymfony.com/grants/foo', [], [])
+        );
+    }
     public function testInvalidGrantExtension(): void
     {
         $this->expectException(\OAuth2\OAuth2ServerException::class);