diff --git a/changelog.d/6967.bugfix b/changelog.d/6967.bugfix
new file mode 100644
index 0000000000..b65f80cf1d
--- /dev/null
+++ b/changelog.d/6967.bugfix
@@ -0,0 +1 @@
+Fix an issue affecting worker-based deployments where replication would stop working, necessitating a full restart, after joining a large room.
diff --git a/synapse/replication/tcp/streams/_base.py b/synapse/replication/tcp/streams/_base.py
index a8d568b14a..208e8a667b 100644
--- a/synapse/replication/tcp/streams/_base.py
+++ b/synapse/replication/tcp/streams/_base.py
@@ -24,7 +24,7 @@ import attr
 logger = logging.getLogger(__name__)
 
 
-MAX_EVENTS_BEHIND = 10000
+MAX_EVENTS_BEHIND = 500000
 
 BackfillStreamRow = namedtuple(
     "BackfillStreamRow",