diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 815410969..158206aef 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -17,7 +17,7 @@ from synapse.api import errors
 from synapse.api.constants import EventTypes
 from synapse.util import stringutils
 from synapse.util.async import Linearizer
-from synapse.types import get_domain_from_id
+from synapse.types import get_domain_from_id, RoomStreamToken
 from twisted.internet import defer
 from ._base import BaseHandler
 
@@ -198,20 +198,22 @@ class DeviceHandler(BaseHandler):
         """Notify that a user's device(s) has changed. Pokes the notifier, and
         remote servers if the user is local.
         """
-        rooms = yield self.store.get_rooms_for_user(user_id)
-        room_ids = [r.room_id for r in rooms]
+        users_who_share_room = yield self.store.get_users_who_share_room_with_user(
+            user_id
+        )
 
         hosts = set()
         if self.hs.is_mine_id(user_id):
-            for room_id in room_ids:
-                users = yield self.store.get_users_in_room(room_id)
-                hosts.update(get_domain_from_id(u) for u in users)
+            hosts.update(get_domain_from_id(u) for u in users_who_share_room)
             hosts.discard(self.server_name)
 
         position = yield self.store.add_device_change_to_streams(
             user_id, device_ids, list(hosts)
         )
 
+        rooms = yield self.store.get_rooms_for_user(user_id)
+        room_ids = [r.room_id for r in rooms]
+
         yield self.notifier.on_new_event(
             "device_list_key", position, rooms=room_ids,
         )
@@ -243,15 +245,15 @@ class DeviceHandler(BaseHandler):
 
         possibly_changed = set(changed)
         for room_id in rooms_changed:
-            # Fetch (an approximation) of the current state at the time.
-            event_rows, token = yield self.store.get_recent_event_ids_for_room(
-                room_id, end_token=from_token.room_key, limit=1,
-            )
+            # Fetch  the current state at the time.
+            stream_ordering = RoomStreamToken.parse_stream_token(from_token.room_key)
 
-            if event_rows:
-                last_event_id = event_rows[-1]["event_id"]
-                prev_state_ids = yield self.store.get_state_ids_for_event(last_event_id)
-            else:
+            try:
+                event_ids = yield self.store.get_forward_extremeties_for_room(
+                    room_id, stream_ordering=stream_ordering
+                )
+                prev_state_ids = yield self.store.get_state_ids_for_events(event_ids)
+            except:
                 prev_state_ids = {}
 
             current_state_ids = yield self.state.get_current_state_ids(room_id)
@@ -266,13 +268,13 @@ class DeviceHandler(BaseHandler):
                     if not prev_event_id or prev_event_id != event_id:
                         possibly_changed.add(state_key)
 
-        user_ids_changed = set()
-        for other_user_id in possibly_changed:
-            other_rooms = yield self.store.get_rooms_for_user(other_user_id)
-            if room_ids.intersection(e.room_id for e in other_rooms):
-                user_ids_changed.add(other_user_id)
+        users_who_share_room = yield self.store.get_users_who_share_room_with_user(
+            user_id
+        )
 
-        defer.returnValue(user_ids_changed)
+        # Take the intersection of the users whose devices may have changed
+        # and those that actually still share a room with the user
+        defer.returnValue(users_who_share_room & possibly_changed)
 
     @defer.inlineCallbacks
     def _incoming_device_list_update(self, origin, edu_content):
diff --git a/synapse/rest/client/v2_alpha/keys.py b/synapse/rest/client/v2_alpha/keys.py
index f99b53530..6a3cfe84f 100644
--- a/synapse/rest/client/v2_alpha/keys.py
+++ b/synapse/rest/client/v2_alpha/keys.py
@@ -193,7 +193,7 @@ class KeyChangesServlet(RestServlet):
         )
 
         defer.returnValue((200, {
-            "changed": changed
+            "changed": list(changed),
         }))