diff --git a/addons/mass_mailing/wizard/mailing_mailing_test.py b/addons/mass_mailing/wizard/mailing_mailing_test.py
index e2abffe1216..a25edffc5b6 100644
--- a/addons/mass_mailing/wizard/mailing_mailing_test.py
+++ b/addons/mass_mailing/wizard/mailing_mailing_test.py
@@ -1,6 +1,8 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
+from markupsafe import Markup
+
 from odoo import _, fields, models, tools
 
 
@@ -39,7 +41,7 @@ class TestMassMailing(models.TransientModel):
             # Returns a proper error if there is a syntax error with Qweb
             body = mailing._render_field('body_html', record.ids, post_process=True)[record.id]
             preview = mailing._render_field('preview', record.ids, post_process=True)[record.id]
-            full_body = mailing._prepend_preview(body, preview)
+            full_body = mailing._prepend_preview(Markup(body), preview)
             subject = mailing._render_field('subject', record.ids)[record.id]
         else:
             full_body = mailing._prepend_preview(mailing.body_html, mailing.preview)