diff --git a/packages/ui-default/backendlib/markdown-it-xss.js b/packages/ui-default/backendlib/markdown-it-xss.js
index 44098228b..6b4f7c36a 100644
--- a/packages/ui-default/backendlib/markdown-it-xss.js
+++ b/packages/ui-default/backendlib/markdown-it-xss.js
@@ -50,6 +50,7 @@ const xss = new Xss.FilterXSS({
         small: [],
         span: ['class'],
         sub: [],
+        summary: [],
         sup: [],
         strong: [],
         table: ['width', 'border', 'align', 'valign'],