diff --git a/wp-includes/class-IXR.php b/wp-includes/class-IXR.php
index 91b65e96bf..5930f562e4 100644
--- a/wp-includes/class-IXR.php
+++ b/wp-includes/class-IXR.php
@@ -402,7 +402,11 @@ class IXR_Server
     {
         if (!$data) {
             if (isset($_SERVER['REQUEST_METHOD']) && $_SERVER['REQUEST_METHOD'] !== 'POST') {
-            	header('Content-Type: text/plain'); // merged from WP #9093
+                if ( function_exists( 'status_header' ) ) {
+                    status_header( 405 ); // WP #20986
+                    header( 'Allow: POST' );
+                }
+                header('Content-Type: text/plain'); // merged from WP #9093
                 die('XML-RPC server accepts POST requests only.');
             }