diff -r 4d00d0109147 Lib/http/client.py
--- a/Lib/http/client.py	Wed Jan 07 00:37:01 2015 +1000
+++ b/Lib/http/client.py	Tue Jan 06 22:20:48 2015 -0800
@@ -774,6 +774,7 @@
             self.close()
             raise OSError("Tunnel connection failed: %d %s" % (code,
                                                                message.strip()))
+
         while True:
             line = response.fp.readline(_MAXLINE + 1)
             if len(line) > _MAXLINE:
@@ -784,6 +785,9 @@
             if line in (b'\r\n', b'\n', b''):
                 break
 
+            if self.debuglevel > 0:
+                print('header:', line.decode())
+
     def connect(self):
         """Connect to the host and port specified in __init__."""
         self.sock = self._create_connection((self.host,self.port),
diff -r 4d00d0109147 Lib/test/test_httplib.py
--- a/Lib/test/test_httplib.py	Wed Jan 07 00:37:01 2015 +1000
+++ b/Lib/test/test_httplib.py	Tue Jan 06 22:20:48 2015 -0800
@@ -1271,6 +1271,7 @@
         header = self.resp.getheader('No-Such-Header',default=42)
         self.assertEqual(header, 42)
 
+
 class TunnelTests(TestCase):
 
     def test_connect(self):
@@ -1281,8 +1282,8 @@
         )
 
         def create_connection(address, timeout=None, source_address=None):
-            return FakeSocket(response_text, host=address[0],
-                              port=address[1])
+            return FakeSocket(
+                response_text, host=address[0], port=address[1])
 
         conn = client.HTTPConnection('proxy.com')
         conn._create_connection = create_connection
@@ -1314,6 +1315,27 @@
         self.assertTrue(b'CONNECT destination.com' in conn.sock.data)
         self.assertTrue(b'Host: destination.com' in conn.sock.data)
 
+    def test_tunnel_debuglog(self):
+        expected_header = 'X-Dummy: 1'
+        response_text = 'HTTP/1.0 200 OK\r\n{}\r\n\r\n'.format(expected_header)
+
+        def create_connection(address, timeout=None, source_address=None):
+            return FakeSocket(
+                response_text, host=address[0], port=address[1])
+
+        conn = client.HTTPConnection('proxy.com')
+        conn._create_connection = create_connection
+        conn.set_debuglevel(1)
+
+        conn.set_tunnel('destination.com')
+        
+        with support.captured_stdout() as output:
+            conn.request('PUT', '/', '')
+
+        lines = output.getvalue().splitlines()
+        self.assertIn('header: {}'.format(expected_header), lines)
+
+
 @support.reap_threads
 def test_main(verbose=None):
     support.run_unittest(HeaderTests, OfflineTest, BasicTest, TimeoutTest,