@@ -158,7 +158,7 @@ def _call_connection_lost(self, exc):
             # end then it may fail with ERROR_NETNAME_DELETED if we
             # just close our end.  First calling shutdown() seems to
             # cure it, but maybe using DisconnectEx() would be better.
-            if hasattr(self._sock, 'shutdown'):
+            if hasattr(self._sock, 'shutdown') and self._sock.fileno() != -1:
                 self._sock.shutdown(socket.SHUT_RDWR)
             self._sock.close()
             self._sock = None
 
@@ -241,6 +241,14 @@ def test_close_buffer(self):
         test_utils.run_briefly(self.loop)
         self.assertFalse(self.protocol.connection_lost.called)
 
+    def test_close_invalid_sockobj(self):
+        tr = self.socket_transport()
+        self.sock.fileno.return_value = -1
+        tr.close()
+        test_utils.run_briefly(self.loop)
+        self.protocol.connection_lost.assert_called_with(None)
+        self.assertFalse(self.sock.shutdown.called)
+
     @mock.patch('asyncio.base_events.logger')
     def test_fatal_error(self, m_logging):
         tr = self.socket_transport()
 
@@ -0,0 +1 @@
+Fix a crash when closing transports where the underlying socket handle is already invalid on the Proactor event loop.
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Fix a crash when closing transports where the underlying socket handle is already invalid on the Proactor event loop.`