diff --git a/Lib/http/server.py b/Lib/http/server.py
index c4ac703d2da..18a51fe5b77 100644
--- a/Lib/http/server.py
+++ b/Lib/http/server.py
@@ -425,7 +425,7 @@ class BaseHTTPRequestHandler(socketserver.StreamRequestHandler):
         # using _quote_html to prevent Cross Site Scripting attacks (see bug #1100201)
         content = (self.error_message_format %
                    {'code': code, 'message': _quote_html(message), 'explain': explain})
-        self.send_response(code, message)
+        self.send_response(code, shortmsg)
         self.send_header("Content-Type", self.error_content_type)
         self.send_header('Connection', 'close')
         self.end_headers()
diff --git a/Misc/NEWS b/Misc/NEWS
index 5bc17841cda..b96662e893f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -193,6 +193,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #12921: BaseHTTPServer's send_error should send the correct error
+  response message when  send_error includes a message in addition to error
+  status. Patch submitted by Karl.
+
 - Issue #17278: Fix a crash in heapq.heappush() and heapq.heappop() when
   the list is being resized concurrently.