diff --git a/includes/menu.inc b/includes/menu.inc
index 312812aa06b05f89c0b0a4500a005260cbfb600e..a92481634f2ed5c5a2c70d626b6d039d25548ccd 100644
--- a/includes/menu.inc
+++ b/includes/menu.inc
@@ -387,7 +387,9 @@ function menu_execute_active_handler($path = NULL) {
   if (_menu_site_is_offline()) {
     return MENU_SITE_OFFLINE;
   }
-  if (variable_get('menu_rebuild_needed', FALSE)) {
+  // Rebuild if we know it's needed, or if the menu masks are missing which
+  // occurs rarely, likely due to a race condition of multiple rebuilds.
+  if (variable_get('menu_rebuild_needed', FALSE) || !variable_get('menu_masks', array())) {
     menu_rebuild();
   }
   if ($router_item = menu_get_item($path)) {