diff --git a/Lib/http/server.py b/Lib/http/server.py
index 6aacbbd..1d193f8 100644
--- a/Lib/http/server.py
+++ b/Lib/http/server.py
@@ -355,6 +355,7 @@
 
         """
         self.send_response_only(100)
+        self.flush_headers()
         return True
 
     def handle_one_request(self):
@@ -432,7 +433,8 @@
             self.wfile.write(content.encode('UTF-8', 'replace'))
 
     def send_response(self, code, message=None):
-        """Send the response header and log the response code.
+        """Add the response header to the headers buffer and log the
+        response code.
 
         Also send two standard headers with the server software
         version and the current date.
@@ -451,11 +453,14 @@
             else:
                 message = ''
         if self.request_version != 'HTTP/0.9':
-            self.wfile.write(("%s %d %s\r\n" %
-                              (self.protocol_version, code, message)).encode('latin-1', 'strict'))
+            if not hasattr(self, '_headers_buffer'):
+                self._headers_buffer = []
+            self._headers_buffer.append(("%s %d %s\r\n" %
+                    (self.protocol_version, code, message)).encode(
+                        'latin-1', 'strict'))
 
     def send_header(self, keyword, value):
-        """Send a MIME header."""
+        """Send a MIME header to the headers buffer."""
         if self.request_version != 'HTTP/0.9':
             if not hasattr(self, '_headers_buffer'):
                 self._headers_buffer = []
@@ -472,6 +477,10 @@
         """Send the blank line ending the MIME headers."""
         if self.request_version != 'HTTP/0.9':
             self._headers_buffer.append(b"\r\n")
+            self.flush_headers()
+
+    def flush_headers(self):
+        if hasattr(self, '_headers_buffer'):
             self.wfile.write(b"".join(self._headers_buffer))
             self._headers_buffer = []
 
@@ -1081,6 +1090,7 @@
             env.setdefault(k, "")
 
         self.send_response(200, "Script output follows")
+        self.flush_headers()
 
         decoded_query = query.replace('+', ' ')
 
diff --git a/Lib/test/test_httpservers.py b/Lib/test/test_httpservers.py
index 39ebc26..1bbaf0e 100644
--- a/Lib/test/test_httpservers.py
+++ b/Lib/test/test_httpservers.py
@@ -461,6 +461,23 @@
         self.send_error(417)
         return False
 
+
+class AuditableBytesIO:
+
+    def __init__(self):
+        self.datas = []
+
+    def write(self, data):
+        self.datas.append(data)
+
+    def getData(self):
+        return b''.join(self.datas)
+
+    @property
+    def numWrites(self):
+        return len(self.datas)
+
+
 class BaseHTTPRequestHandlerTestCase(unittest.TestCase):
     """Test the functionality of the BaseHTTPServer.
 
@@ -527,27 +544,49 @@
         self.verify_get_called()
         self.assertEqual(result[-1], b'<html><body>Data</body></html>\r\n')
 
-    def test_header_buffering(self):
-
-        def _readAndReseek(f):
-            pos = f.tell()
-            f.seek(0)
-            data = f.read()
-            f.seek(pos)
-            return data
+    def test_header_buffering_of_send_error(self):
 
         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'
+        output = AuditableBytesIO()
+        handler = SocketlessRequestHandler()
+        handler.rfile = input
+        handler.wfile = output
+        handler.request_version = 'HTTP/1.1'
+        handler.requestline = ''
+        handler.command = None
 
-        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')
+        handler.send_error(418)
+        self.assertEqual(output.numWrites, 2)
+
+    def test_header_buffering_of_send_response_only(self):
+
+        input = BytesIO(b'GET / HTTP/1.1\r\n\r\n')
+        output = AuditableBytesIO()
+        handler = SocketlessRequestHandler()
+        handler.rfile = input
+        handler.wfile = output
+        handler.request_version = 'HTTP/1.1'
+
+        handler.send_response_only(418)
+        self.assertEqual(output.numWrites, 0)
+        handler.end_headers()
+        self.assertEqual(output.numWrites, 1)
+
+    def test_header_buffering_of_send_header(self):
+
+        input = BytesIO(b'GET / HTTP/1.1\r\n\r\n')
+        output = AuditableBytesIO()
+        handler = SocketlessRequestHandler()
+        handler.rfile = input
+        handler.wfile = output
+        handler.request_version = 'HTTP/1.1'
+
+        handler.send_header('Foo', 'foo')
+        handler.send_header('bar', 'bar')
+        self.assertEqual(output.numWrites, 0)
+        handler.end_headers()
+        self.assertEqual(output.getData(), b'Foo: foo\r\nbar: bar\r\n\r\n')
+        self.assertEqual(output.numWrites, 1)
 
     def test_header_unbuffered_when_continue(self):