diff --git a/libagent/ssh/protocol.py b/libagent/ssh/protocol.py
index 4c2af8f..2c3e8d2 100644
--- a/libagent/ssh/protocol.py
+++ b/libagent/ssh/protocol.py
@@ -167,6 +167,6 @@ class Handler:
         return util.frame(code, data)
 
 
-def _unsupported_extension():
+def _unsupported_extension(buf):
     code = util.pack('B', msg_code('SSH_AGENT_EXTENSION_FAILURE'))
     return util.frame(code)