diff --git a/nixos/modules/services/misc/klipper.nix b/nixos/modules/services/misc/klipper.nix
index f0972f8caff4..d9eef161eb72 100644
--- a/nixos/modules/services/misc/klipper.nix
+++ b/nixos/modules/services/misc/klipper.nix
@@ -113,6 +113,7 @@ in
               '';
               serial = lib.mkOption {
                 type = lib.types.nullOr path;
+                default = null;
                 description = "Path to serial port this printer is connected to. Leave `null` to derive it from `service.klipper.settings`.";
               };
               configFile = lib.mkOption {