diff --git a/synapse/storage/prepare_database.py b/synapse/storage/prepare_database.py
index eaba699e2..72b670b83 100644
--- a/synapse/storage/prepare_database.py
+++ b/synapse/storage/prepare_database.py
@@ -25,7 +25,7 @@ logger = logging.getLogger(__name__)
 
 # Remember to update this number every time a change is made to database
 # schema files, so the users will be informed on server restarts.
-SCHEMA_VERSION = 42
+SCHEMA_VERSION = 43
 
 dir_path = os.path.abspath(os.path.dirname(__file__))
 
diff --git a/synapse/storage/schema/delta/43/user_share.sql b/synapse/storage/schema/delta/43/user_share.sql
new file mode 100644
index 000000000..f552b6eb7
--- /dev/null
+++ b/synapse/storage/schema/delta/43/user_share.sql
@@ -0,0 +1,32 @@
+/* Copyright 2017 Vector Creations 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.
+ */
+
+-- Table keeping track of who shares a room with who. We only keep track
+-- of this for local users, so `user_id` is local users only (but we do keep track
+-- of which remote users share a room)
+CREATE TABLE users_who_share_rooms (
+    user_id TEXT NOT NULL,
+    other_user_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    share_private BOOLEAN NOT NULL  -- is the shared room private? i.e. they share a private room
+);
+
+
+CREATE UNIQUE INDEX users_who_share_rooms_u_idx ON users_who_share_rooms(user_id, other_user_id);
+CREATE INDEX users_who_share_rooms_r_idx ON users_who_share_rooms(room_id, user_id);
+
+
+-- Make sure that we popualte the table initially
+UPDATE user_directory_stream_pos SET stream_id = NULL;