diff --git a/aleksis/apps/chronos/managers.py b/aleksis/apps/chronos/managers.py
index d537dd457e344b43de60f19e1063be9bfc1dfc2e..d1fc3b8525c85fdc354f48d68d207b8e81dab319 100644
--- a/aleksis/apps/chronos/managers.py
+++ b/aleksis/apps/chronos/managers.py
@@ -9,6 +9,7 @@ from django.db.models.fields import DateField
 from django.db.models.functions import Concat
 
 from calendarweek import CalendarWeek
+from polymorphic.managers import PolymorphicQuerySet
 
 from aleksis.apps.chronos.util.date import week_weekday_from_date, week_weekday_to_date
 from aleksis.core.managers import DateRangeQuerySetMixin, SchoolTermRelatedQuerySet
@@ -861,7 +862,7 @@ class RoomPropertiesMixin:
         return sep.join([room.short_name for room in self.get_rooms()])
 
 
-class LessonEventQuerySet(QuerySet):
+class LessonEventQuerySet(PolymorphicQuerySet):
     """Queryset with special query methods for lesson events."""
 
     def for_teacher(self, teacher: Union[int, Person]):
diff --git a/aleksis/apps/chronos/models.py b/aleksis/apps/chronos/models.py
index ae323ccc7ce63f17e9c1224754cc4198f27304d6..052067f5465e127133888104e169cabff5b7148b 100644
--- a/aleksis/apps/chronos/models.py
+++ b/aleksis/apps/chronos/models.py
@@ -65,8 +65,8 @@ from aleksis.apps.cursus import models as cursus_models
 from aleksis.apps.cursus.models import Course
 from aleksis.apps.resint.models import LiveDocument
 from aleksis.core.managers import (
-    AlekSISBaseManagerWithoutMigrations,
     CurrentSiteManagerWithoutMigrations,
+    PolymorphicCurrentSiteManager,
 )
 from aleksis.core.mixins import (
     ExtensibleModel,
@@ -1374,7 +1374,7 @@ class LessonEvent(CalendarEvent):
     name = "lesson"
     verbose_name = _("Lessons")
 
-    objects = AlekSISBaseManagerWithoutMigrations.from_queryset(LessonEventQuerySet)()
+    objects = PolymorphicCurrentSiteManager.from_queryset(LessonEventQuerySet)()
 
     title = models.CharField(verbose_name=_("Name"), max_length=255, blank=True)