diff --git a/modules/backend/classes/AuthManager.php b/modules/backend/classes/AuthManager.php
index d77a3d0c0..c6eefb701 100644
--- a/modules/backend/classes/AuthManager.php
+++ b/modules/backend/classes/AuthManager.php
@@ -144,7 +144,10 @@ class AuthManager extends RainAuthManager
         $tabs = [];
 
         foreach ($this->listPermissions() as $permission) {
-            $tab = isset($permission->tab) ? $permission->tab : null;
+            $tab = isset($permission->tab)
+                ? $permission->tab
+                : 'backend::lang.form.undefined_tab';
+
             if (!array_key_exists($tab, $tabs)) {
                 $tabs[$tab] = [];
             }