diff --git a/sjrpc/core/protocols/rpc.py b/sjrpc/core/protocols/rpc.py
index 1b8b614f46f385b11744395ba7248c8e35fc98e6..79d457c2c82650aed1013cdbbb759324bd832c5a 100644
--- a/sjrpc/core/protocols/rpc.py
+++ b/sjrpc/core/protocols/rpc.py
@@ -55,7 +55,7 @@ class RpcProtocol(object):
 
     def shutdown(self):
         # Release all waiting calls from this rpc:
-        for cid in self._calls:
+        for cid in self._calls.keys():
             err = {'exception': 'RpcError',
                    'message': 'Connection reset by peer'}
             self._handle_response({'id': cid, 'return': None, 'error': err})