diff --git a/proposals/utils/stepper.py b/proposals/utils/stepper.py
index 7702b33a..314fb0d0 100644
--- a/proposals/utils/stepper.py
+++ b/proposals/utils/stepper.py
@@ -36,7 +36,7 @@ def __init__(
         # which item is current
         self.request = request
         self.items = []
-        self.current_item_ancestors = None
+        self.current_item_ancestors = []
 
         self.check_all(self.starting_checkers)