diff --git a/wp-includes/class-IXR.php b/wp-includes/class-IXR.php
index 00f4a0eb8..a4bcfbd57 100644
--- a/wp-includes/class-IXR.php
+++ b/wp-includes/class-IXR.php
@@ -301,6 +301,7 @@ class IXR_Server {
         if (!$data) {
             global $HTTP_RAW_POST_DATA;
             if (!$HTTP_RAW_POST_DATA) {
+               header( 'Content-Type: text/plain' );
                die('XML-RPC server accepts POST requests only.');
             }
             $data = $HTTP_RAW_POST_DATA;