diff --git a/djrill/tests/mock_backend.py b/djrill/tests/mock_backend.py
index a806282..bc46689 100644
--- a/djrill/tests/mock_backend.py
+++ b/djrill/tests/mock_backend.py
@@ -1,5 +1,7 @@
 import json
 from mock import patch
+import requests
+import six
 
 from django.test import TestCase
 
@@ -11,15 +13,13 @@ from .utils import override_settings
 class DjrillBackendMockAPITestCase(TestCase):
     """TestCase that uses Djrill EmailBackend with a mocked Mandrill API"""
 
-    class MockResponse:
+    class MockResponse(requests.Response):
         """requests.post return value mock sufficient for DjrillBackend"""
-        def __init__(self, status_code=200, content="{}", json=None):
+        def __init__(self, status_code=200, raw=six.b("{}"), encoding='utf-8'):
+            super(DjrillBackendMockAPITestCase.MockResponse, self).__init__()
             self.status_code = status_code
-            self.content = content
-            self._json = json if json is not None else ['']
-
-        def json(self):
-            return self._json
+            self.encoding = encoding
+            self.raw = six.BytesIO(raw)
 
     def setUp(self):
         self.patch = patch('requests.post', autospec=True)
diff --git a/djrill/tests/test_mandrill_send.py b/djrill/tests/test_mandrill_send.py
index 403584a..0d3b47a 100644
--- a/djrill/tests/test_mandrill_send.py
+++ b/djrill/tests/test_mandrill_send.py
@@ -6,7 +6,9 @@ from base64 import b64decode
 from datetime import date, datetime, timedelta, tzinfo
 from email.mime.base import MIMEBase
 from email.mime.image import MIMEImage
+import json
 import os
+import six
 
 from django.core import mail
 from django.core.exceptions import ImproperlyConfigured
@@ -466,7 +468,7 @@ class DjrillMandrillFeatureTests(DjrillBackendMockAPITestCase):
     def test_send_attaches_mandrill_response(self):
         """ The mandrill_response should be attached to the message when it is sent """
         response = [{'mandrill_response': 'would_be_here'}]
-        self.mock_post.return_value = self.MockResponse(json=response)
+        self.mock_post.return_value = self.MockResponse(raw=six.b(json.dumps(response)))
         msg = mail.EmailMessage('Subject', 'Message', 'from@example.com', ['to1@example.com'],)
         sent = msg.send()
         self.assertEqual(sent, 1)
diff --git a/docs/contributing.rst b/docs/contributing.rst
index 54956ff..a3e2a81 100644
--- a/docs/contributing.rst
+++ b/docs/contributing.rst
@@ -45,7 +45,8 @@ combinations of Django and Python versions. (Full list in
 The included tests verify that Djrill constructs the expected Mandrill API
 calls, without actually calling Mandrill or sending any email. So the tests
 don't require a Mandrill API key, but they *do* require
-`mock <http://www.voidspace.org.uk/python/mock/index.html>`_ (``pip install mock``).
+`mock <http://www.voidspace.org.uk/python/mock/index.html>`_
+and `six <https://pythonhosted.org/six/>`_ (``pip install mock six``).
 
 To run the tests, either::
 
diff --git a/setup.py b/setup.py
index 3e77cc8..2c5ef2e 100644
--- a/setup.py
+++ b/setup.py
@@ -32,7 +32,7 @@ setup(
     install_requires=["requests>=1.0.0", "django>=1.3"],
     include_package_data=True,
     test_suite="runtests.runtests",
-    tests_require=["mock"],
+    tests_require=["mock", "six"],
     classifiers=[
         "Programming Language :: Python",
         "Programming Language :: Python :: Implementation :: PyPy",