diff --git a/src/Symfony/Component/ErrorRenderer/Exception/FlattenException.php b/src/Symfony/Component/ErrorRenderer/Exception/FlattenException.php
index 0ecbb31a74..669a6652b3 100644
--- a/src/Symfony/Component/ErrorRenderer/Exception/FlattenException.php
+++ b/src/Symfony/Component/ErrorRenderer/Exception/FlattenException.php
@@ -24,7 +24,7 @@ use Symfony\Component\HttpKernel\Exception\HttpExceptionInterface;
  *
  * @author Fabien Potencier <fabien@symfony.com>
  */
-final class FlattenException extends LegacyFlattenException
+class FlattenException extends LegacyFlattenException
 {
     private $title;
     private $message;