diff --git a/mitogen/core.py b/mitogen/core.py
index 1a4e88a1..ec4d5fa8 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()