diff --git a/undar-mode.el b/undar-mode.el
index c7aff4f..895df0f 100644
--- a/undar-mode.el
+++ b/undar-mode.el
@@ -89,7 +89,7 @@
   (setq-local indent-line-function 'c-indent-line))
 
 ;;;###autoload
-(add-to-list 'auto-mode-alist '("\\.undar\\'" . undar-mode))
+(add-to-list 'auto-mode-alist '("\\.ul\\'" . undar-mode))
 
 (provide 'undar-mode)
 ;;; undar-mode.el ends here