diff --git a/lass/1systems/radio/source.nix b/lass/1systems/radio/source.nix
new file mode 100644
index 000000000..4acdb0c26
--- /dev/null
+++ b/lass/1systems/radio/source.nix
@@ -0,0 +1,6 @@
+{ lib, pkgs, test, ... }: let
+  npkgs = lib.importJSON ../../../krebs/nixpkgs-unstable.json;
+in if test then {} else {
+  nixpkgs.git.ref = lib.mkForce npkgs.rev;
+  nixpkgs-unstable = lib.mkForce { file = "/var/empty"; };
+}