diff --git a/Lib/ssl.py b/Lib/ssl.py
index 9d63d12..0161efa 100644
--- a/Lib/ssl.py
+++ b/Lib/ssl.py
@@ -140,6 +140,10 @@
         self.do_handshake_on_connect = do_handshake_on_connect
         self.suppress_ragged_eofs = suppress_ragged_eofs
 
+    def dup(self):
+        raise NotImplemented("Can't dup() %s instances" %
+                             self.__class__.__name__)
+
     def _checkClosed(self, msg=None):
         # raise an exception here if you wish to check for spurious closes
         pass