diff --git a/synapse/replication/tcp/commands.py b/synapse/replication/tcp/commands.py

index f26aee83cb..c7880d4b63 100644
--- a/synapse/replication/tcp/commands.py
+++ b/synapse/replication/tcp/commands.py
@@ -210,7 +210,10 @@ class ReplicateCommand(Command):
 
 class UserSyncCommand(Command):
     """Sent by the client to inform the server that a user has started or
-    stopped syncing. Used to calculate presence on the master.
+    stopped syncing on this process.
+
+    This is used by the process handling presence (typically the master) to
+    calculate who is online and who is not.
 
     Includes a timestamp of when the last user sync was.
 
@@ -218,7 +221,7 @@ class UserSyncCommand(Command):
 
         USER_SYNC <instance_id> <user_id> <state> <last_sync_ms>
 
-    Where <state> is either "start" or "stop"
+    Where <state> is either "start" or "end"
     """
 
     NAME = "USER_SYNC"