diff --git a/engine/apps/api/tests/test_schedules.py b/engine/apps/api/tests/test_schedules.py
index 19537391..13ef0825 100644
--- a/engine/apps/api/tests/test_schedules.py
+++ b/engine/apps/api/tests/test_schedules.py
@@ -985,6 +985,8 @@ def test_merging_same_shift_events(
     user_a = make_user_for_organization(organization)
     user_b = make_user_for_organization(organization)
     user_c = make_user_for_organization(organization, role=Role.VIEWER)
+    # clear users pks <-> organization cache (persisting between tests)
+    memoized_users_in_ical.cache_clear()
 
     data = {
         "start": start_date + timezone.timedelta(hours=10),
diff --git a/engine/apps/schedules/models/on_call_schedule.py b/engine/apps/schedules/models/on_call_schedule.py
index b3d72911..24aa8d0d 100644
--- a/engine/apps/schedules/models/on_call_schedule.py
+++ b/engine/apps/schedules/models/on_call_schedule.py
@@ -654,6 +654,7 @@ class OnCallScheduleWeb(OnCallSchedule):
                 for g in rolling_groups
                 if g is not None
             ),
+            set(),
         )
         return users
 
diff --git a/engine/apps/schedules/tests/test_on_call_schedule.py b/engine/apps/schedules/tests/test_on_call_schedule.py
index bb9699e7..8bb079f4 100644
--- a/engine/apps/schedules/tests/test_on_call_schedule.py
+++ b/engine/apps/schedules/tests/test_on_call_schedule.py
@@ -271,6 +271,8 @@ def test_final_schedule_events(make_organization, make_user_for_organization, ma
     start_date = now - timezone.timedelta(days=7)
 
     user_a, user_b, user_c, user_d, user_e = (make_user_for_organization(organization, username=i) for i in "ABCDE")
+    # clear users pks <-> organization cache (persisting between tests)
+    memoized_users_in_ical.cache_clear()
 
     shifts = (
         # user, priority, start time (h), duration (hs)
@@ -370,6 +372,8 @@ def test_final_schedule_splitting_events(
     start_date = now - timezone.timedelta(days=7)
 
     user_a, user_b, user_c = (make_user_for_organization(organization, username=i) for i in "ABC")
+    # clear users pks <-> organization cache (persisting between tests)
+    memoized_users_in_ical.cache_clear()
 
     shifts = (
         # user, priority, start time (h), duration (hs)
@@ -437,6 +441,8 @@ def test_final_schedule_splitting_same_time_events(
     start_date = now - timezone.timedelta(days=7)
 
     user_a, user_b, user_c = (make_user_for_organization(organization, username=i) for i in "ABC")
+    # clear users pks <-> organization cache (persisting between tests)
+    memoized_users_in_ical.cache_clear()
 
     shifts = (
         # user, priority, start time (h), duration (hs)
@@ -745,6 +751,19 @@ def test_preview_override_shift(make_organization, make_user_for_organization, m
     assert schedule._ical_file_overrides == schedule_overrides_ical
 
 
+@pytest.mark.django_db
+def test_schedule_related_users_empty_schedule(make_organization, make_schedule):
+    organization = make_organization()
+    schedule = make_schedule(
+        organization,
+        schedule_class=OnCallScheduleWeb,
+        name="test_web_schedule",
+    )
+
+    users = schedule.related_users()
+    assert users == set()
+
+
 @pytest.mark.django_db
 def test_schedule_related_users(make_organization, make_user_for_organization, make_on_call_shift, make_schedule):
     organization = make_organization()
@@ -758,6 +777,8 @@ def test_schedule_related_users(make_organization, make_user_for_organization, m
     start_date = now - timezone.timedelta(days=7)
 
     user_a, _, _, user_d, user_e = (make_user_for_organization(organization, username=i) for i in "ABCDE")
+    # clear users pks <-> organization cache (persisting between tests)
+    memoized_users_in_ical.cache_clear()
 
     shifts = (
         # user, priority, start time (h), duration (hs)