diff --git a/config.el b/config.el
index 73a326d..f699ea4 100644
--- a/config.el
+++ b/config.el
@@ -1783,8 +1783,8 @@ current frame."
     "Preserve @ in UID path for Baikal CalDAV compatibility."
     (cl-letf* ((orig-hexify (symbol-function 'url-hexify-string))
                ((symbol-function 'url-hexify-string)
-                (lambda (str)
-                  (replace-regexp-in-string "%40" "@" (funcall orig-hexify str)))))
+                (lambda (str &optional allowed-chars)
+                  (replace-regexp-in-string "%40" "@" (funcall orig-hexify str allowed-chars)))))
       ad-do-it))
 
   ;; Fix #2: Some CalDAV events have nil SUMMARY or missing fields, causing