1 files changed, 5 insertions, 0 deletions
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index fb4dc6d37c..337109f8d5 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -2285,6 +2285,11 @@ class FederationHandler(BaseHandler):
         if event.type == EventTypes.GuestAccess and not context.rejected:
             await self.maybe_kick_guest_users(event)
 
+        # If we are going to send this event over federation we precaclculate
+        # the joined hosts.
+        if event.internal_metadata.get_send_on_behalf_of():
+            await self.event_creation_handler.cache_joined_hosts_for_event(event)
+
         return context
 
     async def _check_for_soft_fail(