diff --git a/src/Symfony/Component/Form/FormConfigInterface.php b/src/Symfony/Component/Form/FormConfigInterface.php
index 47a2ac35a8..e66570cf5f 100644
--- a/src/Symfony/Component/Form/FormConfigInterface.php
+++ b/src/Symfony/Component/Form/FormConfigInterface.php
@@ -167,7 +167,7 @@ interface FormConfigInterface
     /**
      * Returns the class of the form data or null if the data is scalar or an array.
      *
-     * @return string The data class or null
+     * @return null|string The data class or null
      */
     public function getDataClass();