(regexp-opt-group): Compute HALF2 properly.

1 files changed, 4 insertions, 1 deletions

diff --git a/lisp/emacs-lisp/regexp-opt.el b/lisp/emacs-lisp/regexp-opt.el
index b746c8a22f3..ea80801b610 100644
--- a/lisp/emacs-lisp/regexp-opt.el
+++ b/lisp/emacs-lisp/regexp-opt.el
@@ -223,7 +223,10 @@ so we can use character sets rather than grouping parenthesis."
               ;; particular letter and those that do not, and recurse on them.
               (let* ((char (char-to-string (string-to-char (car strings))))
                      (half1 (all-completions char strings))
-                     (half2 (nthcdr (length half1) strings)))
+                     (half2 strings))
+                ;; Remove from HALF2 whatever is in HALF1.
+                (dolist (elt half1)
+                  (setq half2 (delq elt half2)))
                 (concat open-group
                         (regexp-opt-group half1)
                         "\\|" (regexp-opt-group half2)