diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/helpers.py b/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/helpers.py
index 77ddad740865..c7a2a29ee3dc 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/helpers.py
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/helpers.py
@@ -8,4 +8,8 @@ def get_qualified_name(
 ) -> str:
     module_name = getattr(module, "__name__", method.__module__)
     method_name = getattr(method, "__qualname__", method.__name__)
-    return f"{module_name}.{method_name}"
+    name = f"{module_name}.{method_name}"
+    assert name.startswith("nixos_rebuild"), (
+        f"Non-internal module '{name}' called with 'get_qualified_name'"
+    )
+    return name