1 files changed, 19 insertions, 12 deletions

diff --git a/lisp/dired-aux.el b/lisp/dired-aux.el
index e83bb0fd5e6..6af1984dc2f 100644
--- a/lisp/dired-aux.el
+++ b/lisp/dired-aux.el
@@ -43,7 +43,9 @@
 (defun dired-diff (file &optional switches)
   "Compare file at point with file FILE using `diff'.
 FILE defaults to the file at the mark.
-The prompted-for file is the first file given to `diff'."
+The prompted-for file is the first file given to `diff'.
+With prefix arg, prompt for second argument SWITCHES,
+ which is options for `diff'."
   (interactive
    (let ((default (if (mark t)
                       (save-excursion (goto-char (mark t))
@@ -54,23 +56,28 @@ The prompted-for file is the first file given to `diff'."
                                        (concat "(default " default ") ")
                                      ""))
                            (dired-current-directory) default t)
-           (if (fboundp 'diff-read-switches)
-               (diff-read-switches "Options for diff: ")))))
-  (if switches                          ; Emacs 19's diff has but two
-      (diff file (dired-get-filename t) switches) ; args (yet ;-)
-    (diff file (dired-get-filename t))))
+           (if current-prefix-arg
+               (read-string "Options for diff: "
+                            (if (stringp diff-switches)
+                                diff-switches
+                              (mapconcat 'identity diff-switches " ")))))))
+  (diff file (dired-get-filename t) switches))
 
 ;;;###autoload
 (defun dired-backup-diff (&optional switches)
   "Diff this file with its backup file or vice versa.
 Uses the latest backup, if there are several numerical backups.
 If this file is a backup, diff it with its original.
-The backup file is the first file given to `diff'."
-  (interactive (list (if (fboundp 'diff-read-switches)
-                         (diff-read-switches "Diff with switches: "))))
-  (if switches
-      (diff-backup (dired-get-filename) switches)
-    (diff-backup (dired-get-filename))))
+The backup file is the first file given to `diff'.
+With prefix arg, prompt for argument SWITCHES which is options for `diff'."
+  (interactive
+    (if current-prefix-arg
+        (list (read-string "Options for diff: "
+                           (if (stringp diff-switches)
+                               diff-switches
+                             (mapconcat 'identity diff-switches " "))))
+      nil))
+  (diff-backup (dired-get-filename) switches))
 
 (defun dired-do-chxxx (attribute-name program op-symbol arg)
   ;; Change file attributes (mode, group, owner) of marked files and