diff --git a/synapse/federation/transaction_queue.py b/synapse/federation/transaction_queue.py
index fe787abaeb..1f0b67f5f8 100644
--- a/synapse/federation/transaction_queue.py
+++ b/synapse/federation/transaction_queue.py
@@ -175,7 +175,7 @@ class TransactionQueue(object):
                 def handle_event(event):
                     # Only send events for this server.
                     send_on_behalf_of = event.internal_metadata.get_send_on_behalf_of()
-                    is_mine = self.is_mine_id(event.event_id)
+                    is_mine = self.is_mine_id(event.sender)
                     if not is_mine and send_on_behalf_of is None:
                         return
 
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index fcaf7530b0..f89dabb9eb 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -2293,6 +2293,10 @@ class FederationHandler(BaseHandler):
 
             EventValidator().validate_new(event)
 
+            # We need to tell the transaction queue to send this out, even
+            # though the sender isn't a local user.
+            event.internal_metadata.send_on_behalf_of = self.hs.hostname
+
             try:
                 yield self.auth.check_from_context(room_version, event, context)
             except AuthError as e:
@@ -2342,6 +2346,10 @@ class FederationHandler(BaseHandler):
             raise e
         yield self._check_signature(event, context)
 
+        # We need to tell the transaction queue to send this out, even
+        # though the sender isn't a local user.
+        event.internal_metadata.send_on_behalf_of = get_domain_from_id(event.sender)
+
         # XXX we send the invite here, but send_membership_event also sends it,
         # so we end up making two requests. I think this is redundant.
         returned_invite = yield self.send_invite(origin, event)