diff --git a/aleksis/apps/untis/util/mysql/importers/substitutions.py b/aleksis/apps/untis/util/mysql/importers/substitutions.py
index 3a38458f78e47d0e72fb6e7269378c1dd908c883..42f51a3eb0dededc37b6278e715355960bf6c8e5 100644
--- a/aleksis/apps/untis/util/mysql/importers/substitutions.py
+++ b/aleksis/apps/untis/util/mysql/importers/substitutions.py
@@ -177,6 +177,8 @@ def import_substitutions(
                 room = room_old if not room_new and room_old else room_new
                 subject = subject_old if not subject_new else subject_new
                 teachers = [teacher_old] if not teacher_new else [teacher_new]
+                if not teacher_new and not teacher_old:
+                    teachers = []
 
                 (extra_lesson, created,) = (
                     chronos_models.ExtraLesson.objects.select_related(None)