diff --git a/synapse/replication/tcp/streams.py b/synapse/replication/tcp/streams.py
index 4c60bf79f9..07d99dd63c 100644
--- a/synapse/replication/tcp/streams.py
+++ b/synapse/replication/tcp/streams.py
@@ -33,7 +33,7 @@ import logging
 logger = logging.getLogger(__name__)
 
 
-MAX_EVENTS_BEHIND = 10000
+MAX_EVENTS_BEHIND = 500000
 
 
 EventStreamRow = namedtuple("EventStreamRow", (