diff --git a/python/m5/config.py b/python/m5/config.py
index 30ce340f6..e260c57a7 100644
--- a/python/m5/config.py
+++ b/python/m5/config.py
@@ -1285,7 +1285,7 @@ class NullSimObject(object):
         pass
 
     def _convert(cls, value):
-        if value == Nxone:
+        if value == None:
             return
 
         if isinstance(value, cls):