diff --git a/addons/product/product.py b/addons/product/product.py
index 6bee68c2ba6..f82e5791fd7 100644
--- a/addons/product/product.py
+++ b/addons/product/product.py
@@ -250,7 +250,9 @@ class product_template(osv.osv):
                 result[product.id] = {field:False}
             result[product.id]['seller_delay'] = 1
             if product.seller_ids:
-                partner_list = sorted([(partner_id.sequence, partner_id) for partner_id in  product.seller_ids if partner_id and partner_id.sequence])
+                partner_list = sorted([(partner_id.sequence, partner_id)
+                                       for partner_id in  product.seller_ids
+                                       if partner_id and isinstance(partner_id.sequence, (int, long))])
                 main_supplier = partner_list and partner_list[0] and partner_list[0][1] or False
                 result[product.id]['seller_delay'] =  main_supplier and main_supplier.delay or 1
                 result[product.id]['seller_qty'] =  main_supplier and main_supplier.qty or 0.0