diff --git a/Lib/ssl.py b/Lib/ssl.py
index 38aa389..d1d9866 100644
--- a/Lib/ssl.py
+++ b/Lib/ssl.py
@@ -884,8 +884,8 @@
             return self._sslobj.session_reused
 
     def dup(self):
-        raise NotImplemented("Can't dup() %s instances" %
-                             self.__class__.__name__)
+        raise NotImplementedError("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