diff --git a/mitogen/core.py b/mitogen/core.py
index 1a4e88a1285865822e84d87ac89acc91dc87da45..ec4d5fa8b94a7743e4775f2fef8116a6e8a0efec 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -938,7 +938,6 @@ class Broker(object):
     shutdown_timeout = 3.0
 
     def __init__(self):
-        self.on_shutdown = []
         self._alive = True
         self._queue = Queue.Queue()
         self._readers = set()