diff --git a/psutil/__init__.py b/psutil/__init__.py
index 6a5a5eedf..7ba00b3cb 100644
--- a/psutil/__init__.py
+++ b/psutil/__init__.py
@@ -1302,9 +1302,9 @@ def wait(self, timeout=None):
 # The valid attr names which can be processed by Process.as_dict().
 _as_dict_attrnames = set(
     [x for x in dir(Process) if not x.startswith('_') and x not in
-     ['send_signal', 'suspend', 'resume', 'terminate', 'kill', 'wait',
+     {'send_signal', 'suspend', 'resume', 'terminate', 'kill', 'wait',
       'is_running', 'as_dict', 'parent', 'parents', 'children', 'rlimit',
-      'memory_info_ex', 'oneshot']])
+      'memory_info_ex', 'oneshot'}])
 
 
 # =====================================================================