diff --git a/biscuit/apps/untis/util.py b/biscuit/apps/untis/util.py
index f985189c32ed973fd1b5b355259e6fff93264137..ac72d93022ba9bbc39cc0347594c0ee454b52000 100644
--- a/biscuit/apps/untis/util.py
+++ b/biscuit/apps/untis/util.py
@@ -72,8 +72,8 @@ def untis_import_xml(request, untis_xml):
             'name': name})
 
         try:
-            class_.owners = [Person.objects.get(
-                short_name=class_teacher_short_name)]
+            class_.owners.set([Person.objects.get(
+                short_name=class_teacher_short_name)])
             class_.save()
         except Person.DoesNotExist:
             messages.warning(request, _('Could not set class teacher of %s to %s.') % (