diff --git a/channels/generic/websockets.py b/channels/generic/websockets.py
index 7797e9a..6c0820f 100644
--- a/channels/generic/websockets.py
+++ b/channels/generic/websockets.py
@@ -1,4 +1,4 @@
-import json
+from django.core.serializers.json import json, DjangoJSONEncoder
 
 from ..channel import Group, Channel
 from ..auth import channel_session_user_from_http
@@ -222,4 +222,4 @@ class WebsocketDemultiplexer(JsonWebsocketConsumer):
         return {"text": json.dumps({
             "stream": stream,
             "payload": payload,
-        })}
+        }, cls=DjangoJSONEncoder)}
diff --git a/tox.ini b/tox.ini
index 69a082a..fc0d7b4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -18,7 +18,7 @@ deps =
     six
     redis==2.10.5
     py27: mock
-    flake8: flake8
+    flake8: flake8>=2.0,<3.0
     isort: isort
     django-18: Django>=1.8,<1.9
     django-19: Django>=1.9,<1.10