1 files changed, 14 insertions, 6 deletions

diff --git a/lisp/textmodes/ispell.el b/lisp/textmodes/ispell.el
index 424a83c1713..f667525397c 100644
--- a/lisp/textmodes/ispell.el
+++ b/lisp/textmodes/ispell.el
@@ -3006,15 +3006,23 @@ amount for last line processed."
                                      (marker-position ispell-region-end))))
                 (let* ((ispell-start (point))
                        (ispell-end (min (point-at-eol) reg-end))
+                       ;; See if line must be prefixed by comment string to let ispell know this is
+                       ;; part of a comment string.  This is only supported in some modes.
+                       ;; In particular, this is not supported in autoconf mode where adding the
+                       ;; comment string messes everything up because ispell tries to spellcheck the
+                       ;; `dnl' string header causing misalignments in some cases (debbugs.gnu.org: #12768).
+                       (add-comment (and in-comment
+                                         (not (string= in-comment "dnl "))
+                                         in-comment))
                        (string (ispell-get-line
-                                ispell-start ispell-end in-comment)))
+                                ispell-start ispell-end add-comment)))
                   (ispell-print-if-debug
                    (format
-                    "ispell-region: string pos (%s->%s), eol: %s, [in-comment]: [%s], [string]: [%s]\n"
-                    ispell-start ispell-end (point-at-eol) in-comment string))
-                  (if in-comment                ; account for comment chars added
-                      (setq ispell-start (- ispell-start (length in-comment))
-                            in-comment nil))
+                    "ispell-region: string pos (%s->%s), eol: %s, [in-comment]: [%s], [add-comment]: [%s], [string]: [%s]\n"
+                    ispell-start ispell-end (point-at-eol) in-comment add-comment string))
+                  (if add-comment               ; account for comment chars added
+                      (setq ispell-start (- ispell-start (length add-comment))
+                            add-comment nil))
                   (setq ispell-end (point)) ; "end" tracks region retrieved.
                   (if string            ; there is something to spell check!
                       ;; (special start end)