diff --git a/Lib/test/test_httplib.py b/Lib/test/test_httplib.py
index 4abff60..5fb4592 100644
--- a/Lib/test/test_httplib.py
+++ b/Lib/test/test_httplib.py
@@ -10,6 +10,7 @@
 import warnings
 
 import unittest
+from unittest import mock
 TestCase = unittest.TestCase
 
 from test import support
@@ -2051,6 +2052,23 @@ def test_connect_with_tunnel(self):
         # This test should be removed when CONNECT gets the HTTP/1.1 blessing
         self.assertNotIn(b'Host: proxy.com', self.conn.sock.data)
 
+    def test_tunnel_connect_single_send_connection_setup(self):
+        """Regresstion test for https://bugs.python.org/issue43332."""
+        with mock.patch.object(self.conn, 'send') as mock_send:
+            self.conn.set_tunnel('destination.com')
+            self.conn.connect()
+            self.conn.request('GET', '/')
+        mock_send.assert_called()
+        # Likely 2, but this test only cares about the first.
+        self.assertGreater(
+                len(mock_send.mock_calls), 1,
+                msg=f'unexpected number of send calls: {mock_send.mock_calls}')
+        proxy_setup_data_sent = mock_send.mock_calls[0][1][0]
+        self.assertIn(b'CONNECT destination.com', proxy_setup_data_sent)
+        self.assertTrue(
+                proxy_setup_data_sent.endswith(b'\r\n\r\n'),
+                msg=f'unexpected proxy data sent {proxy_setup_data_sent!r}')
+
     def test_connect_put_request(self):
         self.conn.set_tunnel('destination.com')
         self.conn.request('PUT', '/', '')