diff --git a/lib/module.nix b/lib/module.nix
index db05055..1600c50 100644
--- a/lib/module.nix
+++ b/lib/module.nix
@@ -205,6 +205,7 @@
   };
 
   nixtestSubmodule = {config, ...}: {
+    _file = ./module.nix;
     options = {
       base = mkOption {
         type = types.str;