diff --git a/nixos/tests/nar-serve.nix b/nixos/tests/nar-serve.nix
index bb95ccb36911..f6197567b822 100644
--- a/nixos/tests/nar-serve.nix
+++ b/nixos/tests/nar-serve.nix
@@ -27,6 +27,8 @@ import ./make-test-python.nix (
         };
       };
     testScript = ''
+      import os
+
       start_all()
 
       # Create a fake cache with Nginx service the static files