diff --git a/rest_framework_bulk/drf3/serializers.py b/rest_framework_bulk/drf3/serializers.py
index 9098829..31fff46 100644
--- a/rest_framework_bulk/drf3/serializers.py
+++ b/rest_framework_bulk/drf3/serializers.py
@@ -1,4 +1,6 @@
 from __future__ import print_function, unicode_literals
+import inspect
+
 from rest_framework.exceptions import ValidationError
 from rest_framework.serializers import ListSerializer
 
@@ -41,6 +43,10 @@ def update(self, queryset, all_validated_data):
             for i in all_validated_data
         }
 
+        if not all((bool(i) and not inspect.isclass(i)
+                    for i in all_validated_data_by_id.keys())):
+            raise ValidationError('')
+
         # since this method is given a queryset which can have many
         # model instances, first find all objects to update
         # and only then update the models
diff --git a/rest_framework_bulk/tests/test_generics.py b/rest_framework_bulk/tests/test_generics.py
index 51bdb15..6838bf4 100644
--- a/rest_framework_bulk/tests/test_generics.py
+++ b/rest_framework_bulk/tests/test_generics.py
@@ -1,6 +1,5 @@
 from __future__ import unicode_literals, print_function
 import json
-import unittest
 
 from django.core.urlresolvers import reverse
 from django.test import TestCase
@@ -85,7 +84,6 @@ def test_put(self):
             ]
         )
 
-    @unittest.skip('')
     def test_put_without_update_key(self):
         """
         Test that PUT request updates all submitted resources.
@@ -94,6 +92,7 @@ def test_put_without_update_key(self):
             '',
             json.dumps([
                 {'contents': 'foo', 'number': 3},
+                {'contents': 'rainbows', 'number': 4},  # multiple objects without id
                 {'contents': 'bar', 'number': 4, 'id': 555},  # non-existing id
             ]),
             content_type='application/json',