diff --git a/aleksis/apps/chronos/managers.py b/aleksis/apps/chronos/managers.py
index b9530c8224750d9f1705187e4234951db6647bd7..5adae5cb2600b4a28bb630710a251fec5e676a99 100644
--- a/aleksis/apps/chronos/managers.py
+++ b/aleksis/apps/chronos/managers.py
@@ -522,7 +522,7 @@ class SupervisionQuerySet(ValidityRangeRelatedQuerySet, WeekQuerySetMixin):
 
     def filter_by_weekday(self, weekday: int):
         """Filter supervisions by weekday."""
-        self.filter(
+        return self.filter(
             Q(break_item__before_period__weekday=weekday)
             | Q(break_item__after_period__weekday=weekday)
         )
diff --git a/aleksis/apps/chronos/util/build.py b/aleksis/apps/chronos/util/build.py
index db23417ddcb0e57b5f8e054b60f1edd4dbe463de..cee7aae94782c082b0ae1928007e7e0683913ea1 100644
--- a/aleksis/apps/chronos/util/build.py
+++ b/aleksis/apps/chronos/util/build.py
@@ -129,7 +129,7 @@ def build_timetable(
         )
 
         if is_person:
-            supervisions.filter_by_weekday(date_ref.weekday())
+            supervisions = supervisions.filter_by_weekday(date_ref.weekday())
 
         supervisions_per_period_after = {}
         for supervision in supervisions: