diff --git a/blocks/tag_youtube/block_tag_youtube.php b/blocks/tag_youtube/block_tag_youtube.php
index 08110478b03..14815dff8a8 100644
--- a/blocks/tag_youtube/block_tag_youtube.php
+++ b/blocks/tag_youtube/block_tag_youtube.php
@@ -161,7 +161,7 @@ class block_tag_youtube extends block_base {
             $text .= '<tr>';
             $text .= '<td>';
             $text .= '<a href="'. $video['url'] . '">';
-            $text .= '<img class="youtube-thumb" title="'.$video['title'].'" style="padding:3px;" src="' . $video['thumbnail_url'] . '"/>' ;
+            $text .= '<img alt="'.s($video['title']).'" class="youtube-thumb" title="'.$video['title'].'" style="padding:3px;" src="' . $video['thumbnail_url'] . '"/>' ;
             $text .= "</a>";
             $text .= "</td>";
             $text .= '<td>';