diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 36f6eb75e..f96561c1f 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -572,7 +572,7 @@ class TransportLayerClient(object):
         return self.client.post_json(
             destination=destination,
             path=path,
-            args=requester_user_id,
+            args={"requester_user_id": requester_user_id},
             data=content,
             ignore_backoff=True,
         )