diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 6648f2daef..00c756df5d 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -1242,6 +1242,7 @@ static void resolve_deltas(void)
 	base_cache_limit = delta_base_cache_limit * nr_threads;
 	if (nr_threads > 1 || getenv("GIT_FORCE_THREADS")) {
 		init_thread();
+		work_lock();
 		for (i = 0; i < nr_threads; i++) {
 			int ret = pthread_create(&thread_data[i].thread, NULL,
 						 threaded_second_pass, thread_data + i);
@@ -1249,6 +1250,7 @@ static void resolve_deltas(void)
 				die(_("unable to create thread: %s"),
 				    strerror(ret));
 		}
+		work_unlock();
 		for (i = 0; i < nr_threads; i++)
 			pthread_join(thread_data[i].thread, NULL);
 		cleanup_thread();