diff --git a/py34/bacpypes/service/cov.py b/py34/bacpypes/service/cov.py
index 0288713..79b7c0b 100644
--- a/py34/bacpypes/service/cov.py
+++ b/py34/bacpypes/service/cov.py
@@ -90,7 +90,7 @@ class Subscription(OneShotTask, DebugContents):
         'lifetime',
         )
 
-    def __init__(self, obj_ref, client_addr, proc_id, obj_id, confirmed, lifetime):
+    def __init__(self, obj_ref, client_addr, proc_id, obj_id, confirmed, lifetime=0):
         if _debug: Subscription._debug("__init__ %r %r %r %r %r %r", obj_ref, client_addr, proc_id, obj_id, confirmed, lifetime)
         OneShotTask.__init__(self)