diff --git a/aleksis/apps/lesrooster/models.py b/aleksis/apps/lesrooster/models.py
index 56696a640117ac4cb01d091a335299e213197e43..23c44e615ab088cb811be2a1a8c884a207d28b50 100644
--- a/aleksis/apps/lesrooster/models.py
+++ b/aleksis/apps/lesrooster/models.py
@@ -339,7 +339,8 @@ class Lesson(TeacherPropertiesMixin, RoomPropertiesMixin, ExtensibleModel):
 
         lesson_event.save()
 
-        lesson_event.groups.set(self.course.groups.all())
+        if self.course:
+            lesson_event.groups.set(self.course.groups.all())
         lesson_event.teachers.set(self.teachers.all())
         lesson_event.rooms.set(self.rooms.all())