modified   .dir-locals.el
@@ -42,12 +42,8 @@
      ;; For use with 'bug-reference-prog-mode'.  Extra bug-reference
      ;; configuration should be done in your Emacs user configuration file;
      ;; refer to (info (guix) The Perfect Setup).
-     (eval . (setq-local
-              ;; #8545, guix/guix#8545, guix/guix!8545, but not !8545
-              bug-reference-bug-regexp
-              (rx (group (or (seq (zero-or-more "guix/guix") "#")
-                             (seq (one-or-more "guix/guix") "!"))
-                         (group (one-or-more digit))))))
+     (bug-reference-bug-regexp . (rx (group (seq (? "guix/guix") (or "#" "!"))
+                                            (group (one-or-more digit)))))
      (bug-reference-url-format . "https://codeberg.org/guix/guix/issues/%s")
 
      (eval . (add-to-list 'completion-ignored-extensions ".go"))