diff --git a/src/Extension/RuntimeExtensionInterface.php b/src/Extension/RuntimeExtensionInterface.php
index 63bc3b1ab10..9d8d4da3573 100644
--- a/src/Extension/RuntimeExtensionInterface.php
+++ b/src/Extension/RuntimeExtensionInterface.php
@@ -12,6 +12,8 @@
 namespace Twig\Extension;
 
 /**
+ * Marks a class that contains the code of filters, functions or tests, so that it is created only when a template uses them.
+ *
  * @author Grégoire Pineau <lyrixx@lyrixx.info>
  */
 interface RuntimeExtensionInterface