diff --git a/options/auto-upgrade.nix b/options/auto-upgrade.nix
index 18e8544..6d59d18 100644
--- a/options/auto-upgrade.nix
+++ b/options/auto-upgrade.nix
@@ -23,14 +23,14 @@ in
             '';
         };
         gitDeploymentKeyFile = mkOption {
-            type = types.str or null;
+            type = types.nullOr types.str;
             default = null;
             description = mdDoc ''
                 Private SSH key used for the `git pull` operation (if `gitPull` is enabled).
             '';
         };
         gitUser = mkOption {
-            type = types.str or null;
+            type = types.nullOr types.str;
             default = null;
             description = mdDoc ''
                 User used for the `git pull` operation (if `gitPull` is enabled).