diff --git a/IPython/zmq/tests/test_message_spec.py b/IPython/zmq/tests/test_message_spec.py
index 6c42791..ae84166 100644
--- a/IPython/zmq/tests/test_message_spec.py
+++ b/IPython/zmq/tests/test_message_spec.py
@@ -184,6 +184,7 @@ class CompleteReply(Reference):
 
 class PyIn(Reference):
     code = Unicode()
+    execution_count = Integer()
 
 
 PyErr = ExecuteReplyError