Avoid AlreadyCalledError from EDU sending failures

1 files changed, 2 insertions, 1 deletions

diff --git a/synapse/federation/replication.py b/synapse/federation/replication.py

index 38ae360bcd..7868575a2e 100644
--- a/synapse/federation/replication.py
+++ b/synapse/federation/replication.py
@@ -541,7 +541,8 @@ class _TransactionQueue(object):
         )
 
         def eb(failure):
-            deferred.errback(failure)
+            if not deferred.called:
+                deferred.errback(failure)
         self._attempt_new_transaction(destination).addErrback(eb)
 
         return deferred