diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index 1d2fbca0e53..4b5c21973bc 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -2336,6 +2336,7 @@ Call FUN with two args (BEG and END) for each hunk."
   (let ((inhibit-read-only t))
     (undo arg)))
 
+;;;###autoload
 (defcustom diff-add-log-use-relative-names nil
   "Use relative file names when generating ChangeLog skeletons.
 The files will be relative to the root directory of the VC