diff --git a/guppylang/module.py b/guppylang/module.py
index 11c96400..a6680d68 100644
--- a/guppylang/module.py
+++ b/guppylang/module.py
@@ -76,6 +76,7 @@ def __init__(self, name: str, import_builtins: bool = True):
         self._globals = Globals({}, {}, {}, {})
         self._imported_globals = Globals.default()
         self._imported_checked_defs = {}
+        self._checked = False
         self._compiled = False
         self._compiled_hugr = None
         self._instance_func_buffer = None