diff --git a/src/Response.php b/src/Response.php
index f8a2788205..3ad27fde3b 100644
--- a/src/Response.php
+++ b/src/Response.php
@@ -70,6 +70,7 @@ class Response extends AbstractMessage implements ResponseInterface
     const STATUS_CODE_428 = 428;
     const STATUS_CODE_429 = 429;
     const STATUS_CODE_431 = 431;
+    const STATUS_CODE_451 = 451;
     const STATUS_CODE_500 = 500;
     const STATUS_CODE_501 = 501;
     const STATUS_CODE_502 = 502;
@@ -137,6 +138,7 @@ class Response extends AbstractMessage implements ResponseInterface
         428 => 'Precondition Required',
         429 => 'Too Many Requests',
         431 => 'Request Header Fields Too Large',
+        451 => 'Unavailable For Legal Reasons',
         // SERVER ERROR
         500 => 'Internal Server Error',
         501 => 'Not Implemented',