aleksis/apps/matrix/filters.py

 from django.utils.translation import gettext as _
 
-from django_filters import ModelChoiceFilter, ModelMultipleChoiceFilter
+from django_filters import FilterSet, ModelChoiceFilter, ModelMultipleChoiceFilter
 from material import Layout, Row
 
 from aleksis.core.filters import MultipleCharFilter
 from aleksis.core.models import Group, GroupType, SchoolTerm
 
 
-class GroupMatrixRoomFilter:
+class GroupMatrixRoomFilter(FilterSet):
     """Custom filter for groups on Matrix room overview."""
 
     school_term = ModelChoiceFilter(queryset=SchoolTerm.objects.all())