diff --git a/wp-ajax.php b/wp-ajax.php
index ae38391f5..ee7b25a75 100644
--- a/wp-ajax.php
+++ b/wp-ajax.php
@@ -16,6 +16,7 @@ define('DOING_AJAX', true);
 require_once('wp-load.php');
 
 @header('Content-Type: text/html; charset=' . get_option('blog_charset'));
+send_nosniff_header();
 
 do_action('ajax_init');