diff --git a/src/knot/zone/backup.c b/src/knot/zone/backup.c
index 2c6885f930..803dcdcef1 100644
--- a/src/knot/zone/backup.c
+++ b/src/knot/zone/backup.c
@@ -509,7 +509,7 @@ int zone_backup(conf_t *conf, zone_t *zone)
 			break;
 		case BACKUP_FORMAT_2:
 		default:
-			backup_zfiles_dir = sprintf_alloc("%s/%s", ctx->backup_dir, "zonefiles");
+			backup_zfiles_dir = dir_file(ctx->backup_dir, "zonefiles");
 			ABORT_IF_ENOMEM(backup_zfiles_dir);
 			zone_name_str = knot_dname_to_str_alloc(zone->name);
 			ABORT_IF_ENOMEM(zone_name_str);