diff --git a/connected.c b/connected.c
index 21c1ebe9fb..b18299fdf0 100644
--- a/connected.c
+++ b/connected.c
@@ -22,14 +22,13 @@ int check_connected(oid_iterate_fn fn, void *cb_data,
 		    struct check_connected_options *opt)
 {
 	struct child_process rev_list = CHILD_PROCESS_INIT;
+	FILE *rev_list_in;
 	struct check_connected_options defaults = CHECK_CONNECTED_INIT;
-	char commit[GIT_MAX_HEXSZ + 1];
 	struct object_id oid;
 	int err = 0;
 	struct packed_git *new_pack = NULL;
 	struct transport *transport;
 	size_t base_len;
-	const unsigned hexsz = the_hash_algo->hexsz;
 
 	if (!opt)
 		opt = &defaults;
@@ -122,7 +121,8 @@ no_promisor_pack_found:
 
 	sigchain_push(SIGPIPE, SIG_IGN);
 
-	commit[hexsz] = '\n';
+	rev_list_in = xfdopen(rev_list.in, "w");
+
 	do {
 		/*
 		 * If index-pack already checked that:
@@ -135,16 +135,17 @@ no_promisor_pack_found:
 		if (new_pack && find_pack_entry_one(oid.hash, new_pack))
 			continue;
 
-		memcpy(commit, oid_to_hex(&oid), hexsz);
-		if (write_in_full(rev_list.in, commit, hexsz + 1) < 0) {
-			if (errno != EPIPE && errno != EINVAL)
-				error_errno(_("failed write to rev-list"));
-			err = -1;
+		if (fprintf(rev_list_in, "%s\n", oid_to_hex(&oid)) < 0)
 			break;
-		}
 	} while (!fn(cb_data, &oid));
 
-	if (close(rev_list.in))
+	if (ferror(rev_list_in) || fflush(rev_list_in)) {
+		if (errno != EPIPE && errno != EINVAL)
+			error_errno(_("failed write to rev-list"));
+		err = -1;
+	}
+
+	if (fclose(rev_list_in))
 		err = error_errno(_("failed to close rev-list's stdin"));
 
 	sigchain_pop(SIGPIPE);
diff --git a/midx.c b/midx.c
index e046d03578..e9b2e1253a 100644
--- a/midx.c
+++ b/midx.c
@@ -1402,6 +1402,7 @@ int midx_repack(struct repository *r, const char *object_dir, size_t batch_size,
 	uint32_t i;
 	unsigned char *include_pack;
 	struct child_process cmd = CHILD_PROCESS_INIT;
+	FILE *cmd_in;
 	struct strbuf base_name = STRBUF_INIT;
 	struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
 
@@ -1454,6 +1455,8 @@ int midx_repack(struct repository *r, const char *object_dir, size_t batch_size,
 		goto cleanup;
 	}
 
+	cmd_in = xfdopen(cmd.in, "w");
+
 	for (i = 0; i < m->num_objects; i++) {
 		struct object_id oid;
 		uint32_t pack_int_id = nth_midxed_pack_int_id(m, i);
@@ -1462,10 +1465,9 @@ int midx_repack(struct repository *r, const char *object_dir, size_t batch_size,
 			continue;
 
 		nth_midxed_object_oid(&oid, m, i);
-		xwrite(cmd.in, oid_to_hex(&oid), the_hash_algo->hexsz);
-		xwrite(cmd.in, "\n", 1);
+		fprintf(cmd_in, "%s\n", oid_to_hex(&oid));
 	}
-	close(cmd.in);
+	fclose(cmd_in);
 
 	if (finish_command(&cmd)) {
 		error(_("could not finish pack-objects"));
diff --git a/upload-pack.c b/upload-pack.c
index 46a5cac0a9..3b858eb457 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -603,9 +603,8 @@ static int do_reachable_revlist(struct child_process *cmd,
 		"rev-list", "--stdin", NULL,
 	};
 	struct object *o;
-	char namebuf[GIT_MAX_HEXSZ + 2]; /* ^ + hash + LF */
+	FILE *cmd_in = NULL;
 	int i;
-	const unsigned hexsz = the_hash_algo->hexsz;
 
 	cmd->argv = argv;
 	cmd->git_cmd = 1;
@@ -623,8 +622,8 @@ static int do_reachable_revlist(struct child_process *cmd,
 	if (start_command(cmd))
 		goto error;
 
-	namebuf[0] = '^';
-	namebuf[hexsz + 1] = '\n';
+	cmd_in = xfdopen(cmd->in, "w");
+
 	for (i = get_max_object_index(); 0 < i; ) {
 		o = get_indexed_object(--i);
 		if (!o)
@@ -633,11 +632,9 @@ static int do_reachable_revlist(struct child_process *cmd,
 			o->flags &= ~TMP_MARK;
 		if (!is_our_ref(o, allow_uor))
 			continue;
-		memcpy(namebuf + 1, oid_to_hex(&o->oid), hexsz);
-		if (write_in_full(cmd->in, namebuf, hexsz + 2) < 0)
+		if (fprintf(cmd_in, "^%s\n", oid_to_hex(&o->oid)) < 0)
 			goto error;
 	}
-	namebuf[hexsz] = '\n';
 	for (i = 0; i < src->nr; i++) {
 		o = src->objects[i].item;
 		if (is_our_ref(o, allow_uor)) {
@@ -647,11 +644,12 @@ static int do_reachable_revlist(struct child_process *cmd,
 		}
 		if (reachable && o->type == OBJ_COMMIT)
 			o->flags |= TMP_MARK;
-		memcpy(namebuf, oid_to_hex(&o->oid), hexsz);
-		if (write_in_full(cmd->in, namebuf, hexsz + 1) < 0)
+		if (fprintf(cmd_in, "%s\n", oid_to_hex(&o->oid)) < 0)
 			goto error;
 	}
-	close(cmd->in);
+	if (ferror(cmd_in) || fflush(cmd_in))
+		goto error;
+	fclose(cmd_in);
 	cmd->in = -1;
 	sigchain_pop(SIGPIPE);
 
@@ -660,8 +658,8 @@ static int do_reachable_revlist(struct child_process *cmd,
 error:
 	sigchain_pop(SIGPIPE);
 
-	if (cmd->in >= 0)
-		close(cmd->in);
+	if (cmd_in)
+		fclose(cmd_in);
 	if (cmd->out >= 0)
 		close(cmd->out);
 	return -1;