diff --git a/nixos/tests/hardened.nix b/nixos/tests/hardened.nix
index f54506224e51..e38834961e13 100644
--- a/nixos/tests/hardened.nix
+++ b/nixos/tests/hardened.nix
@@ -28,7 +28,7 @@ import ./make-test-python.nix ({ pkgs, ... } : {
         };
       };
       boot.extraModulePackages =
-        optional (versionOlder config.boot.kernelPackages.kernel.version "5.6")
+        pkgs.lib.optional (pkgs.lib.versionOlder config.boot.kernelPackages.kernel.version "5.6")
           config.boot.kernelPackages.wireguard;
       boot.kernelModules = [ "wireguard" ];
     };