diff --git a/lib/helpers.nix b/lib/helpers.nix
index 94d4ab08..393ba2ab 100644
--- a/lib/helpers.nix
+++ b/lib/helpers.nix
@@ -86,7 +86,7 @@ rec {
     );
 
     mkInt = default: mkNullable lib.types.int (toString default);
-    mkBool = default: mkNullable lib.types.bool (toString default);
+    mkBool = default: mkNullable lib.types.bool (if default then "true" else "false");
     mkStr = default: mkNullable lib.types.str ''"${default}"'';
   };