diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index 47793c9d978..40801eb5a9d 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -1055,7 +1055,7 @@ them, instead."
 (defvar diff-remembered-defdir nil)
 
 (defun diff-filename-drop-dir (file)
-  (and (string-match "/" file) (substring file (match-end 0))))
+  (and (string-match "[/\\]" file) (substring file (match-end 0))))
 
 (defun diff-merge-strings (ancestor from to)
   "Merge the diff between ANCESTOR and FROM into TO.