diff --git a/lib/plugins/acl/action.php b/lib/plugins/acl/action.php
index 5e186fb618ea2697a5c29db9ab89f1fa298ae7bf..a7226f598c8ef7db825003a8e59a7811f8ccb4a4 100644
--- a/lib/plugins/acl/action.php
+++ b/lib/plugins/acl/action.php
@@ -20,7 +20,7 @@ class action_plugin_acl extends DokuWiki_Action_Plugin {
      * @param Doku_Event_Handler $controller DokuWiki's event controller object
      * @return void
      */
-    public function register(Doku_Event_Handler &$controller) {
+    public function register(Doku_Event_Handler $controller) {
 
         $controller->register_hook('AJAX_CALL_UNKNOWN', 'BEFORE', $this, 'handle_ajax_call_acl');