diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 3e2ee44177..075e2c5aa4 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -226,7 +226,7 @@ static int anti_reference(const char *refname, const struct object_id *oid,
 	return 0;
 }
 
-static int show_abbrev(const struct object_id *oid, void *cb_data)
+static int show_abbrev(const struct object_id *oid, void *cb_data UNUSED)
 {
 	show_rev(NORMAL, oid, NULL);
 	return 0;