diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index c7f021d1ff..5530b8c48f 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -28,14 +28,14 @@ class Filtering(object):
         return result
 
     def add_user_filter(self, user_localpart, user_filter):
-        self._check_valid_filter(user_filter)
+        self.check_valid_filter(user_filter)
         return self.store.add_user_filter(user_localpart, user_filter)
 
     # TODO(paul): surely we should probably add a delete_user_filter or
     #   replace_user_filter at some point? There's no REST API specified for
     #   them however
 
-    def _check_valid_filter(self, user_filter_json):
+    def check_valid_filter(self, user_filter_json):
         """Check if the provided filter is valid.
 
         This inspects all definitions contained within the filter.
@@ -129,52 +129,55 @@ class Filtering(object):
 
 class FilterCollection(object):
     def __init__(self, filter_json):
-        self.filter_json = filter_json
+        self._filter_json = filter_json
 
-        room_filter_json = self.filter_json.get("room", {})
+        room_filter_json = self._filter_json.get("room", {})
 
-        self.room_filter = Filter({
+        self._room_filter = Filter({
             k: v for k, v in room_filter_json.items()
             if k in ("rooms", "not_rooms")
         })
 
-        self.room_timeline_filter = Filter(room_filter_json.get("timeline", {}))
-        self.room_state_filter = Filter(room_filter_json.get("state", {}))
-        self.room_ephemeral_filter = Filter(room_filter_json.get("ephemeral", {}))
-        self.room_account_data = Filter(room_filter_json.get("account_data", {}))
-        self.presence_filter = Filter(self.filter_json.get("presence", {}))
-        self.account_data = Filter(self.filter_json.get("account_data", {}))
+        self._room_timeline_filter = Filter(room_filter_json.get("timeline", {}))
+        self._room_state_filter = Filter(room_filter_json.get("state", {}))
+        self._room_ephemeral_filter = Filter(room_filter_json.get("ephemeral", {}))
+        self._room_account_data = Filter(room_filter_json.get("account_data", {}))
+        self._presence_filter = Filter(filter_json.get("presence", {}))
+        self._account_data = Filter(filter_json.get("account_data", {}))
 
-        self.include_leave = self.filter_json.get("room", {}).get(
+        self.include_leave = filter_json.get("room", {}).get(
             "include_leave", False
         )
 
+    def get_filter_json(self):
+        return self._filter_json
+
     def timeline_limit(self):
-        return self.room_timeline_filter.limit()
+        return self._room_timeline_filter.limit()
 
     def presence_limit(self):
-        return self.presence_filter.limit()
+        return self._presence_filter.limit()
 
     def ephemeral_limit(self):
-        return self.room_ephemeral_filter.limit()
+        return self._room_ephemeral_filter.limit()
 
     def filter_presence(self, events):
-        return self.presence_filter.filter(events)
+        return self._presence_filter.filter(events)
 
     def filter_account_data(self, events):
-        return self.account_data.filter(events)
+        return self._account_data.filter(events)
 
     def filter_room_state(self, events):
-        return self.room_state_filter.filter(self.room_filter.filter(events))
+        return self._room_state_filter.filter(self._room_filter.filter(events))
 
     def filter_room_timeline(self, events):
-        return self.room_timeline_filter.filter(self.room_filter.filter(events))
+        return self._room_timeline_filter.filter(self._room_filter.filter(events))
 
     def filter_room_ephemeral(self, events):
-        return self.room_ephemeral_filter.filter(self.room_filter.filter(events))
+        return self._room_ephemeral_filter.filter(self._room_filter.filter(events))
 
     def filter_room_account_data(self, events):
-        return self.room_account_data.filter(self.room_filter.filter(events))
+        return self._room_account_data.filter(self._room_filter.filter(events))
 
 
 class Filter(object):
@@ -258,3 +261,6 @@ def _matches_wildcard(actual_value, filter_value):
         return actual_value.startswith(type_prefix)
     else:
         return actual_value == filter_value
+
+
+DEFAULT_FILTER_COLLECTION = FilterCollection({})
diff --git a/synapse/rest/client/v2_alpha/filter.py b/synapse/rest/client/v2_alpha/filter.py
index 7695bebc28..7c94f6ec41 100644
--- a/synapse/rest/client/v2_alpha/filter.py
+++ b/synapse/rest/client/v2_alpha/filter.py
@@ -59,7 +59,7 @@ class GetFilterRestServlet(RestServlet):
                 filter_id=filter_id,
             )
 
-            defer.returnValue((200, filter.filter_json))
+            defer.returnValue((200, filter.get_filter_json()))
         except KeyError:
             raise SynapseError(400, "No such filter")
 
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index 4114a7e430..ab924ad9e0 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -24,7 +24,7 @@ from synapse.events import FrozenEvent
 from synapse.events.utils import (
     serialize_event, format_event_for_client_v2_without_room_id,
 )
-from synapse.api.filtering import FilterCollection
+from synapse.api.filtering import FilterCollection, DEFAULT_FILTER_COLLECTION
 from synapse.api.errors import SynapseError
 from ._base import client_v2_patterns
 
@@ -113,20 +113,20 @@ class SyncRestServlet(RestServlet):
             )
         )
 
-        if filter_id and filter_id.startswith('{'):
-            try:
-                filter_object = json.loads(filter_id)
-            except:
-                raise SynapseError(400, "Invalid filter JSON")
-            self.filtering._check_valid_filter(filter_object)
-            filter = FilterCollection(filter_object)
-        else:
-            try:
+        if filter_id:
+            if filter_id.startswith('{'):
+                try:
+                    filter_object = json.loads(filter_id)
+                except:
+                    raise SynapseError(400, "Invalid filter JSON")
+                self.filtering.check_valid_filter(filter_object)
+                filter = FilterCollection(filter_object)
+            else:
                 filter = yield self.filtering.get_user_filter(
                     user.localpart, filter_id
                 )
-            except:
-                filter = FilterCollection({})
+        else:
+            filter = DEFAULT_FILTER_COLLECTION
 
         sync_config = SyncConfig(
             user=user,