1 files changed, 2 insertions, 1 deletions
diff --git a/synapse/replication/tcp/streams/_base.py b/synapse/replication/tcp/streams/_base.py
index b0f87c365b..084604e8b0 100644
--- a/synapse/replication/tcp/streams/_base.py
+++ b/synapse/replication/tcp/streams/_base.py
@@ -104,7 +104,8 @@ class Stream(object):
         implemented by subclasses.
 
         current_token_function is called to get the current token of the underlying
-        stream.
+        stream. It is only meaningful on the process that is the source of the
+        replication stream (ie, usually the master).
 
         update_function is called to get updates for this stream between a pair of
         stream tokens. See the UpdateFunction type definition for more info.