diff --git a/src/keymap.c b/src/keymap.c
index 61c6c1d9fd1..616ab1cbfe2 100644
--- a/src/keymap.c
+++ b/src/keymap.c
@@ -2547,7 +2547,7 @@ static void
 describe_map (map, keys, elt_describer, partial, shadow, seen, nomenu)
      register Lisp_Object map;
      Lisp_Object keys;
-     int (*elt_describer) ();
+     void (*elt_describer) P_ ((Lisp_Object));
      int partial;
      Lisp_Object shadow;
      Lisp_Object *seen;