diff --git a/b_asic/schedule.py b/b_asic/schedule.py
index 925615cbc9c261a3f46fedd4987f631b389cba66..237430a32daaa1fc2bd2fd3650cff01c7f5a615e 100644
--- a/b_asic/schedule.py
+++ b/b_asic/schedule.py
@@ -966,7 +966,7 @@ class Schedule:
 
     def _reset_y_locations(self) -> None:
         """Reset all the y-locations in the schedule to None"""
-        self._y_locations = defaultdict(lambda: None)
+        self._y_locations = defaultdict(_y_locations_default)
 
     def plot(self, ax: Axes, operation_gap: Optional[float] = None) -> None:
         """