diff --git a/addons/website_slides/controllers/main.py b/addons/website_slides/controllers/main.py
index 2e0091b53f1..70f83b18a37 100644
--- a/addons/website_slides/controllers/main.py
+++ b/addons/website_slides/controllers/main.py
@@ -292,10 +292,8 @@ class website_slides(http.Controller):
 
     @http.route(['/slides/add_slide'], type='json', auth='user', methods=['POST'], website=True)
     def create_slide(self, *args, **post):
-        payload = request.httprequest.content_length
-        # payload is total request content size so it's not exact size of file.
-        # already add client validation this is for double check if client alter.
-        if (payload / 1024 / 1024 > 25):
+        file_size = len(post['datas']) * 3 / 4; # base64
+        if (file_size / 1024.0 / 1024.0) > 25:
             return {'error': _('File is too big. File size cannot exceed 25MB')}
 
         values = dict((fname, post[fname]) for fname in [