diff --git a/src/HtmlUtils.js b/src/HtmlUtils.js
index 824f59ab20..9afaf8adfe 100644
--- a/src/HtmlUtils.js
+++ b/src/HtmlUtils.js
@@ -23,6 +23,7 @@ var highlight = require('highlight.js');
 var sanitizeHtmlParams = {
     allowedTags: [
         'font', // custom to matrix. deliberately no h1/h2 to stop people shouting.
+        'del', // for markdown
         'h3', 'h4', 'h5', 'h6', 'blockquote', 'p', 'a', 'ul', 'ol',
         'nl', 'li', 'b', 'i', 'strong', 'em', 'strike', 'code', 'hr', 'br', 'div',
         'table', 'thead', 'caption', 'tbody', 'tr', 'th', 'td', 'pre'