diff --git a/odoo/addons/base/ir/ir_qweb/assetsbundle.py b/odoo/addons/base/ir/ir_qweb/assetsbundle.py
index f2221e9f7cd82..9137e10212a96 100644
--- a/odoo/addons/base/ir/ir_qweb/assetsbundle.py
+++ b/odoo/addons/base/ir/ir_qweb/assetsbundle.py
@@ -201,12 +201,15 @@ def get_attachments(self, type, ignore_version=False):
         return self.env['ir.attachment'].sudo().browse(attachment_ids)
 
     def save_attachment(self, type, content, inc=None):
+        assert type in ('js', 'css')
         ira = self.env['ir.attachment']
 
         fname = '%s%s.%s' % (self.name, ('' if inc is None else '.%s' % inc), type)
+        mimetype = 'application/javascript' if type == 'js' else 'text/css'
         values = {
             'name': "/web/content/%s" % type,
             'datas_fname': fname,
+            'mimetype' : mimetype,
             'res_model': 'ir.ui.view',
             'res_id': False,
             'type': 'binary',