diff --git a/aircox/tests/models/test_schedule.py b/aircox/tests/models/test_schedule.py
index 737185a..6d1a662 100644
--- a/aircox/tests/models/test_schedule.py
+++ b/aircox/tests/models/test_schedule.py
@@ -123,7 +123,7 @@ class TestSchedule:
     def test_diffusions_of_month(self, sched_initials):
         # TODO: test values of initial, rerun
         for schedule in sched_initials:
-            at = schedule.start + timedelta(days=30)
+            at = schedule.date + timedelta(days=30)
             dates = set(schedule.dates_of_month(at))
             episodes, diffusions = schedule.diffusions_of_month(at)