diff --git a/src/python/oftest/illegal_message.py b/src/python/oftest/illegal_message.py
index 2d0ce7b..fa404cf 100644
--- a/src/python/oftest/illegal_message.py
+++ b/src/python/oftest/illegal_message.py
@@ -29,6 +29,7 @@
         of10.ofp_header.__init__(self)
         self.version = of10.OFP_VERSION
         self.type = ILLEGAL_MESSAGE_TYPE
+        self.xid = None
         self.data = ""
         for (k, v) in kwargs.items():
             if hasattr(self, k):