Index: src/wp-includes/functions.php
===================================================================
--- src/wp-includes/functions.php	(revision 36184)
+++ src/wp-includes/functions.php	(working copy)
@@ -1021,6 +1021,7 @@
 			428 => 'Precondition Required',
 			429 => 'Too Many Requests',
 			431 => 'Request Header Fields Too Large',
+			451 => 'Unavailable For Legal Reasons',
 
 			500 => 'Internal Server Error',
 			501 => 'Not Implemented',