diff --git a/aleksis/apps/chronos/managers.py b/aleksis/apps/chronos/managers.py
index ca92c3ebe735ff3d60379d68e93fbcc4d1a5df47..c7bab932913248876f9d5661cb3e7093b7be805c 100644
--- a/aleksis/apps/chronos/managers.py
+++ b/aleksis/apps/chronos/managers.py
@@ -420,8 +420,8 @@ class LessonDataQuerySet(models.QuerySet, WeekQuerySetMixin):
         year = reference._year
         if week < 1:
             year -= 1
-            week = CalendarWeek.get_last_week_of_year(year)
-        elif week > CalendarWeek.get_last_week_of_year(year):
+            week = CalendarWeek.get_last_week_of_year(year).week
+        elif week > CalendarWeek.get_last_week_of_year(year).week:
             year += 1
             week = 1
 
@@ -429,7 +429,7 @@ class LessonDataQuerySet(models.QuerySet, WeekQuerySetMixin):
         # to check whether the validity range has to be changed
         week = CalendarWeek(week=week, year=year)
         next_lesson_period = current_lesson_periods[next_index]
-        next_lesson_period_date = week_weekday_to_date(week, next_lesson_period.period.period)
+        next_lesson_period_date = week_weekday_to_date(week, next_lesson_period.period.weekday)
 
         validity_index = validity_ranges.index(next_lesson_period.lesson.validity)
 
diff --git a/aleksis/apps/chronos/models.py b/aleksis/apps/chronos/models.py
index a883414aad27e5fe01702561e5d15f1b6da30871..209155a4a1c306acfbbf96d099a3e5970d286b86 100644
--- a/aleksis/apps/chronos/models.py
+++ b/aleksis/apps/chronos/models.py
@@ -369,7 +369,7 @@ class Lesson(ValidityRangeRelatedExtensibleModel, GroupPropertiesMixin, TeacherP
         verbose_name_plural = _("Lessons")
 
 
-class LessonSubstitution(ExtensibleModel, WeekRelatedMixin):
+class LessonSubstitution(ExtensibleModel, TeacherPropertiesMixin, WeekRelatedMixin):
     objects = LessonSubstitutionManager.from_queryset(LessonSubstitutionQuerySet)()
 
     week = models.IntegerField(verbose_name=_("Week"), default=CalendarWeek.current_week)
diff --git a/aleksis/apps/chronos/util/build.py b/aleksis/apps/chronos/util/build.py
index d7c189860c376c04a504a0769dcf7023f2b8ab86..185c8f543eac3ac280a1036117414b165044c6e7 100644
--- a/aleksis/apps/chronos/util/build.py
+++ b/aleksis/apps/chronos/util/build.py
@@ -127,7 +127,7 @@ def build_timetable(
 
             for period in range(period_from, period_to + 1):
                 if period not in events_per_period:
-                    events_per_period[period] = [] if is_person else {}
+                    events_per_period[period] = {} if is_week else []
 
                 if is_week and weekday not in events_per_period[period]:
                     events_per_period[period][weekday] = []