diff --git a/IPython/frontend/html/notebook/handlers.py b/IPython/frontend/html/notebook/handlers.py
index 62b3b8275..92752a555 100644
--- a/IPython/frontend/html/notebook/handlers.py
+++ b/IPython/frontend/html/notebook/handlers.py
@@ -30,6 +30,7 @@ from zmq.utils import jsonapi
 from IPython.external.decorator import decorator
 from IPython.zmq.session import Session
 from IPython.lib.security import passwd_check
+from IPython.utils.jsonutil import date_default
 
 try:
     from docutils.core import publish_string
@@ -385,13 +386,13 @@ class ZMQStreamHandler(websocket.WebSocketHandler):
         except KeyError:
             pass
         msg.pop('buffers')
-        return jsonapi.dumps(msg)
+        return jsonapi.dumps(msg, default=date_default)
 
     def _on_zmq_reply(self, msg_list):
         try:
             msg = self._reserialize_reply(msg_list)
-        except:
-            self.application.log.critical("Malformed message: %r" % msg_list)
+        except Exception:
+            self.application.log.critical("Malformed message: %r" % msg_list, exc_info=True)
         else:
             self.write_message(msg)