diff --git a/modules/system/system.api.php b/modules/system/system.api.php
index 5481e8184a56bfeb35254bc34260fcf83b059399..7b7158a4904fb23bbe8fdabe9a9b5f0659f0557b 100644
--- a/modules/system/system.api.php
+++ b/modules/system/system.api.php
@@ -1911,6 +1911,9 @@ function hook_system_info_alter(&$info, $file, $type) {
  *     warning message defined in user_admin_permissions() will be associated
  *     with the permission and displayed with it on the permission
  *     administration page. Defaults to FALSE.
+ *   - warning: (optional) A translated warning message to display on the
+ *     permission administration page. This warning overrides the automatic
+ *     warning generated by 'restrict access' being set to TRUE.
  */
 function hook_permission() {
   return array(