Ticket #21658: 21658.diff

src/wp-includes/link-template.php

@@ -1655 +1655 @@
  *
  */
 function adjacent_posts_rel_link_wp_head() {
-        if ( ! is_single() ) {
+        if ( ! is_single() || is_attachment() ) {
                 return;
         }
         adjacent_posts_rel_link();