diff --git a/modules/nixos/hydra-auto-upgrade.nix b/modules/nixos/hydra-auto-upgrade.nix
index 7faee75..ac26059 100644
--- a/modules/nixos/hydra-auto-upgrade.nix
+++ b/modules/nixos/hydra-auto-upgrade.nix
@@ -11,7 +11,10 @@ in {
     system.hydraAutoUpgrade = {
       enable = lib.mkEnableOption "periodic hydra-based auto upgrade";
       operation = lib.mkOption {
-        type = lib.types.enum ["switch" "boot"];
+        type = lib.types.enum [
+          "switch"
+          "boot"
+        ];
         default = "switch";
       };
       dates = lib.mkOption {