diff --git a/aleksis/apps/chronos/frontend/components/AmendLesson.vue b/aleksis/apps/chronos/frontend/components/AmendLesson.vue
index 9dc8a8ff00d3bf8942707075682d4434e2e9a967..7f06f71bbf16b7c5f55b310c13dd087d58833f11 100644
--- a/aleksis/apps/chronos/frontend/components/AmendLesson.vue
+++ b/aleksis/apps/chronos/frontend/components/AmendLesson.vue
@@ -157,8 +157,8 @@ export default {
       return {
         ...item,
         amends: this.selectedEvent.meta.id,
-        datetimeStart: this.selectedEvent.startDateTime.toUTC().toISO(),
-        datetimeEnd: this.selectedEvent.endDateTime.toUTC().toISO(),
+        datetimeStart: this.$toUTCISO(this.selectedEvent.startDateTime),
+        datetimeEnd: this.$toUTCISO(this.selectedEvent.endDateTime),
         // Normalize cancelled, v-checkbox returns null & does not
         // honor false-value.
         cancelled: item.cancelled ? true : false,
diff --git a/aleksis/apps/chronos/schema/__init__.py b/aleksis/apps/chronos/schema/__init__.py
index 279003489d17818eda4487867de799fb1eeef213..d9194e6718112025b4e41713cd00ff5d043bebf6 100644
--- a/aleksis/apps/chronos/schema/__init__.py
+++ b/aleksis/apps/chronos/schema/__init__.py
@@ -1,5 +1,3 @@
-from datetime import timezone
-
 import graphene
 from graphene_django import DjangoObjectType
 
@@ -60,27 +58,7 @@ class LessonEventType(DjangoObjectType):
     amends = graphene.Field(lambda: LessonEventType, required=False)
 
 
-class DatetimeTimezoneMixin:
-    """Handle datetimes for mutations with CalendarEvent objects.
-
-    This is necessary because the client sends timezone information as
-    ISO string which only includes an offset (+00:00 UTC) and an
-    offset is not a valid timezone. Instead we set UTC as timezone
-    here directly.
-    """
-
-    @classmethod
-    def handle_datetime_start(cls, value, name, info) -> int:
-        value = value.replace(tzinfo=timezone.utc)
-        return value
-
-    @classmethod
-    def handle_datetime_end(cls, value, name, info) -> int:
-        value = value.replace(tzinfo=timezone.utc)
-        return value
-
-
-class AmendLessonBatchCreateMutation(DatetimeTimezoneMixin, BaseBatchCreateMutation):
+class AmendLessonBatchCreateMutation(BaseBatchCreateMutation):
     class Meta:
         model = LessonEvent
         permissions = ("chronos.edit_substitution_rule",)
@@ -104,7 +82,7 @@ class AmendLessonBatchCreateMutation(DatetimeTimezoneMixin, BaseBatchCreateMutat
         return created_objects
 
 
-class AmendLessonBatchPatchMutation(DatetimeTimezoneMixin, BaseBatchPatchMutation):
+class AmendLessonBatchPatchMutation(BaseBatchPatchMutation):
     class Meta:
         model = LessonEvent
         permissions = ("chronos.edit_substitution_rule",)