diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index 502ff1512..269cf2148 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -707,7 +707,7 @@ class MatrixFederationHttpClient(object):
         }
 
         response = yield self._send_request_with_optional_trailing_slash(
-            request, try_trailing_slash_on_400, send_request_args,
+            request, try_trailing_slash_on_400, backoff_on_404, send_request_args,
         )
 
         body = yield _handle_json_response(