diff --git a/aleksis/apps/chronos/managers.py b/aleksis/apps/chronos/managers.py
index e4387402ec83f8887e4d447962e99c0b8385e866..d52c750d5575910fa50299628ab6735ddb7d142b 100644
--- a/aleksis/apps/chronos/managers.py
+++ b/aleksis/apps/chronos/managers.py
@@ -27,21 +27,27 @@ class LessonEventQuerySet(RecurrencePolymorphicQuerySet):
 
     def for_teacher(self, teacher: Union[int, Person]) -> "LessonEventQuerySet":
         """Get all lesson events for a certain person as teacher (including amends)."""
-        amended = self.filter(Q(amended_by__isnull=False) & (Q(teachers=teacher))).values_list(
-            "amended_by__pk", flat=True
-        )
+        from .models import LessonEvent
+
+        amended = LessonEvent.objects.filter(
+            amended_by__isnull=False, teachers=teacher
+        ).values_list("amended_by__pk", flat=True)
         return self.filter(Q(teachers=teacher) | Q(pk__in=amended)).distinct()
 
     def for_participant(self, person: Union[int, Person]) -> "LessonEventQuerySet":
         """Get all lesson events the person participates in (including amends)."""
-        amended = self.filter(Q(amended_by__isnull=False) & Q(groups__members=person)).values_list(
-            "amended_by__pk", flat=True
-        )
+        from .models import LessonEvent
+
+        amended = LessonEvent.objects.filter(
+            amended_by__isnull=False, groups__members=person
+        ).values_list("amended_by__pk", flat=True)
         return self.filter(Q(groups__members=person) | Q(pk__in=amended)).distinct()
 
     def for_group(self, group: Union[int, Group]) -> "LessonEventQuerySet":
         """Get all lesson events for a certain group (including amends/as parent group)."""
-        amended = self.filter(
+        from .models import LessonEvent
+
+        amended = LessonEvent.objects.filter(
             Q(amended_by__isnull=False) & (Q(groups=group) | Q(groups__parent_groups=group))
         ).values_list("amended_by__pk", flat=True)
         return self.filter(
@@ -50,21 +56,27 @@ class LessonEventQuerySet(RecurrencePolymorphicQuerySet):
 
     def for_room(self, room: Union[int, Room]) -> "LessonEventQuerySet":
         """Get all lesson events for a certain room (including amends)."""
-        amended = self.filter(Q(amended_by__isnull=False) & (Q(rooms=room))).values_list(
-            "amended_by__pk", flat=True
-        )
+        from .models import LessonEvent
+
+        amended = LessonEvent.objects.filter(
+            Q(amended_by__isnull=False) & (Q(rooms=room))
+        ).values_list("amended_by__pk", flat=True)
         return self.filter(Q(rooms=room) | Q(pk__in=amended)).distinct()
 
     def for_course(self, course: Union[int, Course]) -> "LessonEventQuerySet":
         """Get all lesson events for a certain course (including amends)."""
-        amended = self.filter(Q(amended_by__isnull=False) & (Q(course=course))).values_list(
+        from .models import LessonEvent
+
+        amended = LessonEvent.objects.filter(amended_by__isnull=False, course=course).values_list(
             "amended_by__pk", flat=True
         )
         return self.filter(Q(course=course) | Q(pk__in=amended)).distinct()
 
     def for_person(self, person: Union[int, Person]) -> "LessonEventQuerySet":
         """Get all lesson events for a certain person (as teacher/participant, including amends)."""
-        amended = self.filter(
+        from .models import LessonEvent
+
+        amended = LessonEvent.objects.filter(
             Q(amended_by__isnull=False) & (Q(teachers=person) | Q(groups__members=person))
         ).values_list("amended_by__pk", flat=True)
         return self.filter(
@@ -78,7 +90,9 @@ class LessonEventQuerySet(RecurrencePolymorphicQuerySet):
         teacher/participant/group owner/parent group owner,
         including those amended.
         """
-        amended = self.filter(
+        from .models import LessonEvent
+
+        amended = LessonEvent.objects.filter(
             Q(amended_by__isnull=False)
             & (
                 Q(teachers=person)