diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 5a8ddc253e..6de6e13b7b 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -27,7 +27,7 @@ from synapse.types import (
 from synapse.util.async import run_on_reactor, ReadWriteLock, Limiter
 from synapse.util.logcontext import preserve_fn, run_in_background
 from synapse.util.metrics import measure_func
-from synapse.util.frozenutils import unfreeze
+from synapse.util.frozenutils import frozendict_json_encoder
 from synapse.util.stringutils import random_string
 from synapse.visibility import filter_events_for_client
 from synapse.replication.http.send_event import send_event_to_master
@@ -678,7 +678,7 @@ class EventCreationHandler(object):
 
         # Ensure that we can round trip before trying to persist in db
         try:
-            dump = simplejson.dumps(unfreeze(event.content))
+            dump = frozendict_json_encoder.encode(event.content)
             simplejson.loads(dump)
         except Exception:
             logger.exception("Failed to encode content: %r", event.content)
diff --git a/synapse/replication/tcp/commands.py b/synapse/replication/tcp/commands.py
index 0005ad5879..12aac3cc6b 100644
--- a/synapse/replication/tcp/commands.py
+++ b/synapse/replication/tcp/commands.py
@@ -24,6 +24,8 @@ import simplejson
 
 logger = logging.getLogger(__name__)
 
+_json_encoder = simplejson.JSONEncoder(namedtuple_as_object=False)
+
 
 class Command(object):
     """The base command class.
@@ -107,7 +109,7 @@ class RdataCommand(Command):
         return " ".join((
             self.stream_name,
             str(self.token) if self.token is not None else "batch",
-            simplejson.dumps(self.row, namedtuple_as_object=False),
+            _json_encoder.encode(self.row),
         ))
 
 
@@ -302,7 +304,7 @@ class InvalidateCacheCommand(Command):
 
     def to_line(self):
         return " ".join((
-            self.cache_func, simplejson.dumps(self.keys, namedtuple_as_object=False)
+            self.cache_func, _json_encoder.encode(self.keys),
         ))
 
 
@@ -334,7 +336,7 @@ class UserIpCommand(Command):
         )
 
     def to_line(self):
-        return self.user_id + " " + simplejson.dumps((
+        return self.user_id + " " + _json_encoder.encode((
             self.access_token, self.ip, self.user_agent, self.device_id,
             self.last_seen,
         ))
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index f3d65f4338..ece5e6c41f 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -14,15 +14,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from synapse.storage.events_worker import EventsWorkerStore
+from collections import OrderedDict, deque, namedtuple
+from functools import wraps
+import logging
 
+import simplejson as json
 from twisted.internet import defer
 
-from synapse.events import USE_FROZEN_DICTS
 
+from synapse.storage.events_worker import EventsWorkerStore
 from synapse.util.async import ObservableDeferred
+from synapse.util.frozenutils import frozendict_json_encoder
 from synapse.util.logcontext import (
-    PreserveLoggingContext, make_deferred_yieldable
+    PreserveLoggingContext, make_deferred_yieldable,
 )
 from synapse.util.logutils import log_function
 from synapse.util.metrics import Measure
@@ -30,16 +34,8 @@ from synapse.api.constants import EventTypes
 from synapse.api.errors import SynapseError
 from synapse.util.caches.descriptors import cached, cachedInlineCallbacks
 from synapse.types import get_domain_from_id
-
-from canonicaljson import encode_canonical_json
-from collections import deque, namedtuple, OrderedDict
-from functools import wraps
-
 import synapse.metrics
 
-import logging
-import simplejson as json
-
 # these are only included to make the type annotations work
 from synapse.events import EventBase    # noqa: F401
 from synapse.events.snapshot import EventContext   # noqa: F401
@@ -71,10 +67,7 @@ state_delta_reuse_delta_counter = metrics.register_counter(
 
 
 def encode_json(json_object):
-    if USE_FROZEN_DICTS:
-        return encode_canonical_json(json_object)
-    else:
-        return json.dumps(json_object, ensure_ascii=False)
+    return frozendict_json_encoder.encode(json_object)
 
 
 class _EventPeristenceQueue(object):
diff --git a/synapse/util/frozenutils.py b/synapse/util/frozenutils.py
index 6322f0f55c..f497b51f4a 100644
--- a/synapse/util/frozenutils.py
+++ b/synapse/util/frozenutils.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 from frozendict import frozendict
+import simplejson as json
 
 
 def freeze(o):
@@ -49,3 +50,21 @@ def unfreeze(o):
         pass
 
     return o
+
+
+def _handle_frozendict(obj):
+    """Helper for EventEncoder. Makes frozendicts serializable by returning
+    the underlying dict
+    """
+    if type(obj) is frozendict:
+        # fishing the protected dict out of the object is a bit nasty,
+        # but we don't really want the overhead of copying the dict.
+        return obj._dict
+    raise TypeError('Object of type %s is not JSON serializable' %
+                    obj.__class__.__name__)
+
+
+# A JSONEncoder which is capable of encoding frozendics without barfing
+frozendict_json_encoder = json.JSONEncoder(
+    default=_handle_frozendict,
+)