Index: Lib/http/server.py
===================================================================
--- Lib/http/server.py	(revision 86610)
+++ Lib/http/server.py	(working copy)
@@ -443,7 +443,10 @@
     def send_header(self, keyword, value):
         """Send a MIME header."""
         if self.request_version != 'HTTP/0.9':
-            self.wfile.write(("%s: %s\r\n" % (keyword, value)).encode('ASCII', 'strict'))
+            if not hasattr(self, '_headers_buffer'):
+                self._headers_buffer = []
+            self._headers_buffer.append(
+                ("%s: %s\r\n" % (keyword, value)).encode('ASCII', 'strict'))
 
         if keyword.lower() == 'connection':
             if value.lower() == 'close':
@@ -454,7 +457,9 @@
     def end_headers(self):
         """Send the blank line ending the MIME headers."""
         if self.request_version != 'HTTP/0.9':
-            self.wfile.write(b"\r\n")
+            self._headers_buffer.append(b"\r\n")
+            self.wfile.write(b"".join(self._headers_buffer))
+            self._headers_buffer = []
 
     def log_request(self, code='-', size='-'):
         """Log an accepted request.
Index: Lib/test/test_httpservers.py
===================================================================
--- Lib/test/test_httpservers.py	(revision 86595)
+++ Lib/test/test_httpservers.py	(working copy)
@@ -476,6 +476,28 @@
         match = self.HTTPResponseMatch.search(response)
         self.assertTrue(match is not None)
 
+    def test_header_buffering(self):
+
+        def _readAndReseek(f):
+            pos = f.tell()
+            f.seek(0)
+            data = f.read()
+            f.seek(pos)
+            return data
+
+        input = BytesIO(b'GET / HTTP/1.1\r\n\r\n')
+        output = BytesIO()
+        self.handler.rfile = input
+        self.handler.wfile = output
+        self.handler.request_version = 'HTTP/1.1'
+
+        self.handler.send_header('Foo', 'foo')
+        self.handler.send_header('bar', 'bar')
+        self.assertEqual(_readAndReseek(output), b'')
+        self.handler.end_headers()
+        self.assertEqual(_readAndReseek(output),
+                         b'Foo: foo\r\nbar: bar\r\n\r\n')
+
     def test_http_1_1(self):
         result = self.send_typical_request(b'GET / HTTP/1.1\r\n\r\n')
         self.verify_http_server_response(result[0])