diff --git a/lisp/vc/emerge.el b/lisp/vc/emerge.el
index 422ed5c0a4d..6ee20bf59ba 100644
--- a/lisp/vc/emerge.el
+++ b/lisp/vc/emerge.el
@@ -2942,6 +2942,7 @@ If some prefix of KEY has a non-prefix definition, it is redefined."
 
 ;; Define a key if it (or a prefix) is not already defined in the map.
 (defun emerge-define-key-if-possible (keymap key definition)
+  (declare (obsolete keymap-set "29.1"))
   ;; look up the present definition of the key
   (let ((present (lookup-key keymap key)))
     (if (integerp present)