diff --git a/synapse/storage/filtering.py b/synapse/storage/filtering.py
index 73f7a078fa..78b1e30945 100644
--- a/synapse/storage/filtering.py
+++ b/synapse/storage/filtering.py
@@ -19,6 +19,7 @@ from ._base import SQLBaseStore
 from synapse.api.errors import SynapseError, Codes
 from synapse.util.caches.descriptors import cachedInlineCallbacks
 
+from canonicaljson import encode_canonical_json
 import simplejson as json
 
 
@@ -46,7 +47,7 @@ class FilteringStore(SQLBaseStore):
         defer.returnValue(json.loads(str(def_json).decode("utf-8")))
 
     def add_user_filter(self, user_localpart, user_filter):
-        def_json = json.dumps(user_filter).encode("utf-8")
+        def_json = encode_canonical_json(user_filter)
 
         # Need an atomic transaction to SELECT the maximal ID so far then
         # INSERT a new one