diff --git a/go/vumitools/tests/test_billing_worker.py b/go/vumitools/tests/test_billing_worker.py
index af5f7dfa3..0bc12cb30 100644
--- a/go/vumitools/tests/test_billing_worker.py
+++ b/go/vumitools/tests/test_billing_worker.py
@@ -49,7 +49,7 @@ def create_transaction(self, account_number, message_id, tag_pool_name,
             "last_modified": "2013-10-30T10:42:51.144745+02:00",
             "status": "Completed",
             "transaction_type": transaction_type,
-            "session_length": session_length
+            "session_length": session_length,
         }