diff --git a/http.c b/http.c
index 62aa995245..39cbd56702 100644
--- a/http.c
+++ b/http.c
@@ -2270,9 +2270,9 @@ int finish_http_pack_request(struct http_pack_request *preq)
 {
 	struct packed_git **lst;
 	struct packed_git *p = preq->target;
-	char *tmp_idx;
-	size_t len;
 	struct child_process ip = CHILD_PROCESS_INIT;
+	int tmpfile_fd;
+	int ret = 0;
 
 	close_pack_index(p);
 
@@ -2284,35 +2284,24 @@ int finish_http_pack_request(struct http_pack_request *preq)
 		lst = &((*lst)->next);
 	*lst = (*lst)->next;
 
-	if (!strip_suffix(preq->tmpfile.buf, ".pack.temp", &len))
-		BUG("pack tmpfile does not end in .pack.temp?");
-	tmp_idx = xstrfmt("%.*s.idx.temp", (int)len, preq->tmpfile.buf);
+	tmpfile_fd = xopen(preq->tmpfile.buf, O_RDONLY);
 
 	argv_array_push(&ip.args, "index-pack");
-	argv_array_pushl(&ip.args, "-o", tmp_idx, NULL);
-	argv_array_push(&ip.args, preq->tmpfile.buf);
+	argv_array_push(&ip.args, "--stdin");
 	ip.git_cmd = 1;
-	ip.no_stdin = 1;
+	ip.in = tmpfile_fd;
 	ip.no_stdout = 1;
 
 	if (run_command(&ip)) {
-		unlink(preq->tmpfile.buf);
-		unlink(tmp_idx);
-		free(tmp_idx);
-		return -1;
-	}
-
-	unlink(sha1_pack_index_name(p->hash));
-
-	if (finalize_object_file(preq->tmpfile.buf, sha1_pack_name(p->hash))
-	 || finalize_object_file(tmp_idx, sha1_pack_index_name(p->hash))) {
-		free(tmp_idx);
-		return -1;
+		ret = -1;
+		goto cleanup;
 	}
 
 	install_packed_git(the_repository, p);
-	free(tmp_idx);
-	return 0;
+cleanup:
+	close(tmpfile_fd);
+	unlink(preq->tmpfile.buf);
+	return ret;
 }
 
 struct http_pack_request *new_http_pack_request(