diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index a333acc4aa..a72c92c62a 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1102,6 +1102,7 @@ class FederationHandler(BaseHandler):
             user_id,
             "leave"
         )
+        event.internal_metadata.outlier = True
         event = self._sign_event(event)
 
         # Try the host that we succesfully called /make_leave/ on first for