diff --git a/synapse/util/frozenutils.py b/synapse/util/frozenutils.py
new file mode 100644
index 0000000000..46d3ab4f7d
--- /dev/null
+++ b/synapse/util/frozenutils.py
@@ -0,0 +1,56 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from frozendict import frozendict
+
+import json
+
+
+def freeze(o):
+    if isinstance(o, dict) or isinstance(o, frozendict):
+        return frozendict({k: freeze(v) for k, v in o.items()})
+
+    if isinstance(o, basestring):
+        return o
+
+    try:
+        return tuple([freeze(i) for i in o])
+    except TypeError:
+        pass
+
+    return o
+
+
+def unfreeze(o):
+    if isinstance(o, frozendict) or isinstance(o, dict):
+        return dict({k: unfreeze(v) for k, v in o.items()})
+
+    if isinstance(o, basestring):
+        return o
+
+    try:
+        return [unfreeze(i) for i in o]
+    except TypeError:
+        pass
+
+    return o
+
+
+class FrozenEncoder(json.JSONEncoder):
+    def default(self, o):
+        if isinstance(o, frozendict):
+            return dict(o)
+
+        return json.JSONEncoder(self, o)
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