diff --git a/addons/website_forum/models/forum.py b/addons/website_forum/models/forum.py
index 1efb7cade15..94df769a88d 100644
--- a/addons/website_forum/models/forum.py
+++ b/addons/website_forum/models/forum.py
@@ -533,7 +533,7 @@ class Post(models.Model):
         question = self.parent_id
         values = {
             'author_id': self.sudo().create_uid.partner_id.id,  # use sudo here because of access to res.users model
-            'body': tools.html2plaintext(self.content),
+            'body': tools.html_sanitize(self.content, strict=True, strip_style=True, strip_classes=True),
             'type': 'comment',
             'subtype': 'mail.mt_comment',
             'date': self.create_date,
diff --git a/openerp/tools/mail.py b/openerp/tools/mail.py
index b1f5768a320..46443481acf 100644
--- a/openerp/tools/mail.py
+++ b/openerp/tools/mail.py
@@ -53,7 +53,7 @@ safe_attrs = clean.defs.safe_attrs | frozenset(
      ])
 
 
-def html_sanitize(src, silent=True, strict=False, strip_style=False):
+def html_sanitize(src, silent=True, strict=False, strip_style=False, strip_classes=False):
     if not src:
         return src
     src = ustr(src, errors='replace')
@@ -88,9 +88,13 @@ def html_sanitize(src, silent=True, strict=False, strip_style=False):
     if strict:
         if etree.LXML_VERSION >= (3, 1, 0):
             # lxml < 3.1.0 does not allow to specify safe_attrs. We keep all attributes in order to keep "style"
+            if strip_classes:
+                current_safe_attrs = safe_attrs - frozenset(['class'])
+            else:
+                current_safe_attrs = safe_attrs
             kwargs.update({
                 'safe_attrs_only': True,
-                'safe_attrs': safe_attrs,
+                'safe_attrs': current_safe_attrs,
             })
     else:
         kwargs['safe_attrs_only'] = False    # keep oe-data attributes + style