diff --git a/python/paddle_serving_server_gpu/web_service.py b/python/paddle_serving_server_gpu/web_service.py
index 8b5aa1a233534cc1ab80fe9a892759ce5a311dcb..9231cfbe8a246adedd4692c56944755dd948fdce 100644
--- a/python/paddle_serving_server_gpu/web_service.py
+++ b/python/paddle_serving_server_gpu/web_service.py
@@ -369,6 +369,6 @@ class WebService(object):
         return feed, fetch
 
     def postprocess(self, feed=[], fetch=[], fetch_map=None):
-        for key in fetch_map.iterkeys():
+        for key in fetch_map:
             fetch_map[key] = fetch_map[key].tolist()
         return fetch_map