diff --git a/lib/src/options/default.nix b/lib/src/options/default.nix
index 4406583..f1d11b7 100644
--- a/lib/src/options/default.nix
+++ b/lib/src/options/default.nix
@@ -47,7 +47,7 @@ lib: {
                 lib.modules.apply.properties definition.value
               );
               normalize = value: {
-                __file__ = definition.__file__;
+                __file__ = definition.__file__ or "<unknown>";
                 inherit value;
               };
             in