1 files changed, 10 insertions, 4 deletions
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index 571eacd343..42cd528908 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -858,22 +858,24 @@ class PresenceEventSource(object):
 
         presence = self.hs.get_handlers().presence_handler
         cachemap = presence._user_cachemap
+
+        max_serial = presence._user_cachemap_latest_serial
+
         clock = self.clock
-        latest_serial = None
+        latest_serial = 0
 
         updates = []
         # TODO(paul): use a DeferredList ? How to limit concurrency.
         for observed_user in cachemap.keys():
             cached = cachemap[observed_user]
 
-            if cached.serial <= from_key:
+            if cached.serial <= from_key or cached.serial > max_serial:
                 continue
 
             if not (yield self.is_visible(observer_user, observed_user)):
                 continue
 
-            if latest_serial is None or cached.serial > latest_serial:
-                latest_serial = cached.serial
+            latest_serial = max(cached.serial, latest_serial)
             updates.append(cached.make_event(user=observed_user, clock=clock))
 
         # TODO(paul): limit
@@ -882,6 +884,10 @@ class PresenceEventSource(object):
             if serial < from_key:
                 break
 
+            if serial > max_serial:
+                continue
+
+            latest_serial = max(latest_serial, serial)
             for u in user_ids:
                 updates.append({
                     "type": "m.presence",