diff --git a/paramiko/packet.py b/paramiko/packet.py
index 1380899..7561649 100644
--- a/paramiko/packet.py
+++ b/paramiko/packet.py
@@ -99,13 +99,6 @@ class Packetizer (object):
         self.__keepalive_last = time.time()
         self.__keepalive_callback = None
         
-    def __del__(self):
-        # this is not guaranteed to be called, but we should try.
-        try:
-            self.__socket.close()
-        except:
-            pass
-
     def set_log(self, log):
         """
         Set the python log object to use for logging.
diff --git a/paramiko/transport.py b/paramiko/transport.py
index 4dd9448..ff3e239 100644
--- a/paramiko/transport.py
+++ b/paramiko/transport.py
@@ -727,7 +727,7 @@ class Transport (threading.Thread):
         @since: fearow
         """
         self.packetizer.set_keepalive(interval,
-            lambda x=self: x.global_request('keepalive@lag.net', wait=False))
+            lambda x=weakref.proxy(self): x.global_request('keepalive@lag.net', wait=False))
 
     def global_request(self, kind, data=None, wait=True):
         """