diff --git a/artiq/protocols/pc_rpc.py b/artiq/protocols/pc_rpc.py
index 0884903f1..1787a2111 100644
--- a/artiq/protocols/pc_rpc.py
+++ b/artiq/protocols/pc_rpc.py
@@ -18,6 +18,7 @@ import threading
 import time
 import logging
 import inspect
+from operator import itemgetter
 
 from artiq.protocols import pyon
 from artiq.protocols.asyncio_server import AsyncioServer as _AsyncioServer