diff --git a/cookbook/security/api_key_authentication.rst b/cookbook/security/api_key_authentication.rst
index e27ef087c90..1d7fa563eca 100644
--- a/cookbook/security/api_key_authentication.rst
+++ b/cookbook/security/api_key_authentication.rst
@@ -215,9 +215,12 @@ Handling Authentication Failure
 
 In order for your ``ApiKeyAuthentication`` to correctly display a 403
 http status when either bad credentials or authentication fails you will 
-need to implement the :class:`Symfony\Component\Security\Http\Authentication\AuthenticationFailureHandlerInterface` on your 
-Authenticator. This will provide a method ``onAuthenticationFailure`` which 
-you can use to create an error ``Response``.
+need to implement the
+:class:`Symfony\Component\Security\Http\Authentication\AuthenticationFailureHandlerInterface`
+on your Authenticator. This will provide a method ``onAuthenticationFailure``
+which you can use to create an error ``Response``.
+
+.. code-block:: php
 
     // src/Acme/HelloBundle/Security/ApiKeyAuthenticator.php
     namespace Acme\HelloBundle\Security;