diff --git a/midx.c b/midx.c
index 0da2faac67..c774cd69c7 100644
--- a/midx.c
+++ b/midx.c
@@ -254,7 +254,7 @@ struct object_id *nth_midxed_object_oid(struct object_id *oid,
 	if (n >= m->num_objects)
 		return NULL;
 
-	oidread(oid, m->chunk_oid_lookup + m->hash_len * n);
+	oidread(oid, m->chunk_oid_lookup + st_mult(m->hash_len, n));
 	return oid;
 }