1 files changed, 13 insertions, 0 deletions

diff --git a/lisp/files.el b/lisp/files.el
index bdd5604417d..84c167f756b 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -1069,6 +1069,19 @@ that are visiting the various files."
                          (with-current-buffer buf
                            (revert-buffer t t)))))
               (with-current-buffer buf
+
+                ;; Check if a formerly read-only file has become
+                ;; writable and vice versa.
+                (let ((read-only (not (file-writable-p buffer-file-name))))
+                  (unless (eq read-only buffer-read-only)
+                    (when (or nowarn
+                              (let ((question 
+                                     (format "File %s is %s on disk.  Change buffer mode? "
+                                             buffer-file-name
+                                             (if read-only "read-only" "writable"))))
+                                (y-or-n-p question)))
+                      (setq buffer-read-only read-only))))
+
                 (when (not (eq (not (null rawfile))
                                (not (null find-file-literally))))
                   (if (buffer-modified-p)