diff --git a/modules/system/system.module b/modules/system/system.module
index 2bbcd7f..595fbaf 100644
--- a/modules/system/system.module
+++ b/modules/system/system.module
@@ -539,7 +539,7 @@ function system_menu() {
     'theme callback' => 'ajax_base_page_theme',
     'type' => MENU_CALLBACK,
     'file path' => 'includes',
-    'file' => 'form.inc',
+    'file' => 'ajax.inc',
   );
   $items['system/timezone'] = array(
     'title' => 'Time zone',