diff -r 69ea73015132 Lib/httplib.py
--- a/Lib/httplib.py	Wed Sep 02 22:07:31 2015 -0400
+++ b/Lib/httplib.py	Fri Sep 04 10:08:56 2015 +1200
@@ -810,7 +810,9 @@
                                        method = self._method)
         (version, code, message) = response._read_status()
 
-        if code != 200:
+        # HTTP/0.9 doesn't support the CONNECT verb, so if httplib has
+        # concluded HTTP/0.9 is being used something has gone wrong.
+        if code != 200 or version == "HTTP/0.9":
             self.close()
             raise socket.error("Tunnel connection failed: %d %s" % (code,
                                                                     message.strip()))
diff -r 69ea73015132 Lib/test/test_httplib.py
--- a/Lib/test/test_httplib.py	Wed Sep 02 22:07:31 2015 -0400
+++ b/Lib/test/test_httplib.py	Fri Sep 04 10:08:56 2015 +1200
@@ -578,6 +578,15 @@
         #self.assertTrue(response[0].closed)
         self.assertTrue(conn.sock.file_closed)
 
+    def test_proxy_tunnel_without_status_line(self):
+        # Issue 17849: If a proxy tunnel is created that does not return
+        # a status code, fail.
+        body = 'hello world'
+        conn = httplib.HTTPConnection('example.com', strict=False)
+        conn.set_tunnel('foo')
+        conn.sock = FakeSocket(body)
+        self.assertRaises(socket.error, conn._tunnel)
+
 class OfflineTest(TestCase):
     def test_responses(self):
         self.assertEqual(httplib.responses[httplib.NOT_FOUND], "Not Found")