diff --git a/django_etesync/serializers.py b/django_etesync/serializers.py
index c5734d2..3b50c36 100644
--- a/django_etesync/serializers.py
+++ b/django_etesync/serializers.py
@@ -203,7 +203,7 @@ class CollectionSerializer(serializers.ModelSerializer):
 
         with transaction.atomic():
             if etag is not None:
-                raise serializers.ValidationError('Stoken is not None')
+                raise serializers.ValidationError('etag is not None')
 
             instance.save()
             main_item = models.CollectionItem.objects.create(
@@ -222,13 +222,9 @@ class CollectionSerializer(serializers.ModelSerializer):
 
     def update(self, instance, validated_data):
         """Function that's called when this serializer is meant to update an item"""
-        etag = validated_data.pop('etag')
         revision_data = validated_data.pop('content')
 
         with transaction.atomic():
-            if etag != instance.etag:
-                raise serializers.ValidationError('Wrong etag. Expected {} got {}'.format(instance.etag, etag))
-
             main_item = instance.main_item
             # We don't have to use select_for_update here because the unique constraint on current guards against
             # the race condition. But it's a good idea because it'll lock and wait rather than fail.
diff --git a/django_etesync/views.py b/django_etesync/views.py
index 235d378..dff1096 100644
--- a/django_etesync/views.py
+++ b/django_etesync/views.py
@@ -163,6 +163,13 @@ class CollectionViewSet(BaseViewSet):
 
     def update(self, request, *args, **kwargs):
         instance = self.get_object()
+
+        stoken = request.GET.get('stoken', None)
+
+        if stoken is not None and stoken != instance.stoken:
+            content = {'code': 'stale_stoken', 'detail': 'Stoken is too old'}
+            return Response(content, status=status.HTTP_400_BAD_REQUEST)
+
         serializer = self.get_serializer(instance, data=request.data)
         serializer.is_valid(raise_exception=True)
         self.perform_update(serializer)