diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index 27b478a1c3..7565d94449 100755
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -275,6 +275,7 @@ def setup():
     hs.get_pusherpool().start()
     hs.get_state_handler().start_caching()
     hs.get_datastore().start_profiling()
+    hs.get_replication_layer().start_pdu_fail_cache()
 
     if config.daemonize:
         print config.pid_file