diff --git a/src/Symfony/Component/HttpKernel/Bundle/Bundle.php b/src/Symfony/Component/HttpKernel/Bundle/Bundle.php
index 2681257e1ac4..96c38223b3f9 100644
--- a/src/Symfony/Component/HttpKernel/Bundle/Bundle.php
+++ b/src/Symfony/Component/HttpKernel/Bundle/Bundle.php
@@ -74,11 +74,11 @@ public function getContainerExtension()
         if (null === $this->extension) {
             $extension = $this->createContainerExtension();
 
-            if (!$extension instanceof ExtensionInterface) {
-                throw new \LogicException(sprintf('Extension %s must implement Symfony\Component\DependencyInjection\Extension\ExtensionInterface.', get_class($extension)));
-            }
-
             if (null !== $extension) {
+                if (!$extension instanceof ExtensionInterface) {
+                    throw new \LogicException(sprintf('Extension %s must implement Symfony\Component\DependencyInjection\Extension\ExtensionInterface.', get_class($extension)));
+                }
+
                 // check naming convention
                 $basename = preg_replace('/Bundle$/', '', $this->getName());
                 $expectedAlias = Container::underscore($basename);