(regexp-opt-depth): Fix off-by-two error.

1 files changed, 3 insertions, 1 deletions

diff --git a/lisp/emacs-lisp/regexp-opt.el b/lisp/emacs-lisp/regexp-opt.el
index b6fac1355c1..894cc4c4be7 100644
--- a/lisp/emacs-lisp/regexp-opt.el
+++ b/lisp/emacs-lisp/regexp-opt.el
@@ -120,7 +120,9 @@ in REGEXP."
     (let ((count 0) start)
       (while (string-match "\\(\\`\\|[^\\]\\)\\\\\\(\\\\\\\\\\)*([^?]"
                            regexp start)
-        (setq count (1+ count) start (match-end 0)))
+        (setq count (1+ count)
+              ;; Go back 2 chars (one for [^?] and one for [^\\]).
+              start (- (match-end 0) 2))
       count)))
 
 ;;; Workhorse functions.