diff --git a/src/Symfony/Component/Serializer/Normalizer/CustomNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/CustomNormalizer.php
index 83c3c14384..e3f09a9436 100644
--- a/src/Symfony/Component/Serializer/Normalizer/CustomNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/CustomNormalizer.php
@@ -59,8 +59,6 @@ class CustomNormalizer extends SerializerAwareNormalizer implements NormalizerIn
      */
     public function supportsDenormalization($data, $type, $format = null)
     {
-        $class = new \ReflectionClass($type);
-
-        return $class->isSubclassOf('Symfony\Component\Serializer\Normalizer\DenormalizableInterface');
+        return is_subclass_of($type, 'Symfony\Component\Serializer\Normalizer\DenormalizableInterface');
     }
 }