diff --git a/builtin/repack.c b/builtin/repack.c
index 094f5a0cc2..7d62959dc2 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c

@@ -413,6 +419,7 @@ static void repack_promisor_objects(struct repository *repo,
 				    const struct pack_objects_args *args,
 				    struct string_list *names)
 {
+	struct write_oid_context ctx;
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	FILE *out;
 	struct strbuf line = STRBUF_INIT;

@@ -427,7 +434,9 @@ static void repack_promisor_objects(struct repository *repo,
 	 * {type -> existing pack order} ordering when computing deltas instead
 	 * of a {type -> size} ordering, which may produce better deltas.
 	 */
-	for_each_packed_object(repo, write_oid, &cmd,
+	ctx.cmd = &cmd;
+	ctx.algop = repo->hash_algo;
+	for_each_packed_object(repo, write_oid, &ctx,
 			       FOR_EACH_OBJECT_PROMISOR_ONLY);