diff --git a/lisp/international/mule.el b/lisp/international/mule.el
index 8754f7f27d7..fa3ad80e2f7 100644
--- a/lisp/international/mule.el
+++ b/lisp/international/mule.el
@@ -1311,8 +1311,8 @@ Internal use only.")
                                     preferred))))))
          (completion-ignore-case t)
          (completion-pcm--delim-wild-regex ; Let "u8" complete to "utf-8".
-          (concat completion-pcm--delim-wild-regex
-                  "\\|\\([[:alpha:]]\\)[[:digit:]]"))
+          (concat "\\(?:" completion-pcm--delim-wild-regex
+                  "\\|\\([[:alpha:]]\\)[[:digit:]]\\)"))
          (cs (completing-read
               (format "Coding system for saving file (default %s): " default)
               combined-table