diff --git a/aleksis/apps/chronos/models.py b/aleksis/apps/chronos/models.py
index 704eee74a8b53e7e3f8bb07a905053fbd60faf5e..0d47ee1efc5f00c95d6d41b07f54bed06f5741fa 100644
--- a/aleksis/apps/chronos/models.py
+++ b/aleksis/apps/chronos/models.py
@@ -553,12 +553,11 @@ class LessonPeriod(ExtensibleModel):
         indexes = [models.Index(fields=["lesson", "period"])]
 
 
-@classmethod
 def for_timetables(cls):
     return cls.objects.filter(show_in_timetables=True)
 
 
-Announcement.for_timetables = for_timetables
+Announcement.class_method(for_timetables)
 Announcement.field(show_in_timetables=BooleanField(verbose_name=_("Show announcement in timetable views?")))