1 files changed, 10 insertions, 7 deletions

diff --git a/lisp/files.el b/lisp/files.el
index be98b3c8562..840ab2f77fa 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -4561,15 +4561,18 @@ See also `auto-save-file-name-p'."
     (let ((buffer-name (buffer-name))
           (limit 0)
           file-name)
-      ;; Eliminate all slashes and backslashes by
-      ;; replacing them with sequences that start with %.
-      ;; Quote % also, to keep distinct names distinct.
-      (while (string-match "[/\\%]" buffer-name limit)
+      ;; Restrict the characters used in the file name to those which
+      ;; are known to be safe on all filesystems, url-encoding the
+      ;; rest.
+      ;; We do this on all platforms, because even if we are not
+      ;; running on DOS/Windows, the current directory may be on a
+      ;; mounted VFAT filesystem, such as a USB memory stick.
+      (while (string-match "[^A-Za-z0-9-_.~#+]" buffer-name limit)
         (let* ((character (aref buffer-name (match-beginning 0)))
                (replacement
-                (cond ((eq character ?%) "%%")
-                      ((eq character ?/) "%+")
-                      ((eq character ?\\) "%-"))))
+                ;; For multibyte characters, this will produce more than
+                ;; 2 hex digits, so is not true URL encoding.
+                (format "%%%02X" character)))
           (setq buffer-name (replace-match replacement t t buffer-name))
           (setq limit (1+ (match-end 0)))))
       ;; Generate the file name.