diff --git a/addons/mail/models/mail_render_mixin.py b/addons/mail/models/mail_render_mixin.py
index 3b650ba38684a9293317ac190250eddafa413877..4b583ed8959f372da659655a08fa15a4a8feae94 100644
--- a/addons/mail/models/mail_render_mixin.py
+++ b/addons/mail/models/mail_render_mixin.py
@@ -5,6 +5,7 @@ import babel
 import copy
 import logging
 import re
+import traceback
 
 from lxml import html
 from markupsafe import Markup
@@ -313,7 +314,7 @@ class MailRenderMixin(models.AbstractModel):
                     group = self.env.ref('mail.group_mail_template_editor')
                     raise AccessError(_('Only users belonging to the "%s" group can modify dynamic templates.', group.name)) from e
                 _logger.info("Failed to render template : %s", template_src, exc_info=True)
-                raise UserError(_("Failed to render QWeb template : %s)", template_src)) from e
+                raise UserError(_("Failed to render QWeb template : %s\n\n%s)", template_src, traceback.format_exc())) from e
             results[record.id] = render_result
 
         return results
diff --git a/addons/mail/wizard/mail_template_preview_views.xml b/addons/mail/wizard/mail_template_preview_views.xml
index 228c97956f5f31de17d1bbc2efba09d87840319d..3cc017101e59b2141cffb3bcdffe05196108a9c4 100644
--- a/addons/mail/wizard/mail_template_preview_views.xml
+++ b/addons/mail/wizard/mail_template_preview_views.xml
@@ -8,7 +8,7 @@
                 <form string="Email Preview">
                     <h3>Preview of <field name="mail_template_id" readonly="1" nolabel="1" options="{'no_open' : True}"/></h3>
                     <div class="alert alert-danger" role="alert" attrs="{'invisible' : [('error_msg', '=', False)]}">
-                        <field name="error_msg" />
+                        <field name="error_msg" widget="text"/>
                     </div>
                     <field name="no_record" invisible="1"/>
                     <div class="container">