diff --git a/src/python/oftest/testutils.py b/src/python/oftest/testutils.py
index 5c3f6f3..6609fc6 100644
--- a/src/python/oftest/testutils.py
+++ b/src/python/oftest/testutils.py
@@ -1152,10 +1152,12 @@
         stats.extend(reply.entries)
     return stats
 
-def get_flow_stats(test, match, table_id=0xff, out_port=ofp.OFPP_NONE):
+def get_flow_stats(test, match, table_id=0xff, out_port=None):
     """
     Retrieve a list of flow stats entries.
     """
+    if out_port == None:
+        out_port = ofp.OFPP_NONE
     req = ofp.message.flow_stats_request(match=match,
                                           table_id=table_id,
                                           out_port=out_port)
@@ -1176,7 +1178,7 @@
     return get_stats(test, req)
 
 def verify_flow_stats(test, match, table_id=0xff,
-                      out_port=ofp.OFPP_NONE,
+                      out_port=None,
                       initial=[],
                       pkts=None, bytes=None):
     """
@@ -1186,6 +1188,9 @@
     get_flow_stats(). If 'initial' is not given the counters are assumed to
     begin at 0.
     """
+    if out_port == None:
+        out_port = ofp.OFPP_NONE
+
     def accumulate(stats):
         pkts_acc = bytes_acc = 0
         for stat in stats: