diff --git a/docs/nix.md b/docs/nix.md
index c53ee92..78a7b90 100644
--- a/docs/nix.md
+++ b/docs/nix.md
@@ -101,7 +101,8 @@ import ./flake {
 
 ### Keep NixOS module interfaces open
 
-NixOS modules accept extra arguments because the module system owns their argument shape.
+Files under `hosts/`, `guests/`, and `modules/` return NixOS modules.
+The NixOS module system owns their argument shape.
 Name each argument the module uses.
 Keep `...` so the module accepts standard module arguments and special arguments.