diff --git a/weight_purchase/models/purchase_order.py b/weight_purchase/models/purchase_order.py
index d27955ce..51efb267 100644
--- a/weight_purchase/models/purchase_order.py
+++ b/weight_purchase/models/purchase_order.py
@@ -1,25 +1,53 @@
-# -*- coding: utf-8 -*-
 # © 2018 Trustcode
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
 
-from odoo import api, models
+from odoo import api, models, _
+from odoo.exceptions import UserError
 
 
 class PurchaseOrder(models.Model):
     _inherit = 'purchase.order'
 
-    @api.onchange('total_despesas', 'total_seguro', 'total_frete')
-    def _onchange_despesas_frete_seguro(self):
+    @api.onchange('total_despesas', 'total_seguro', 'product_id',
+                  'total_frete', 'total_despesas_aduana')
+    def _onchange_frete(self):
         super(PurchaseOrder, self)._onchange_despesas_frete_seguro()
-        full_weight = 0
-        for line in self.order_line:
-            if line.product_id.fiscal_type == 'product':
-                full_weight += (line.product_id.weight * line.product_qty)
+        if self.total_frete == 0 or (
+                not self.fiscal_position_id.fiscal_type == 'import'):
+            return
+        full_weight = self._calc_total_weight()
+        res = {}
         for line in self.order_line:
+            valor_frete = self._calc_percentual_weight(
+                line, full_weight)
+            line.update({
+                'valor_frete': valor_frete
+            })
+            if valor_frete == 0:
+                res = {
+                    'warning': {
+                        'title': _('Warning'),
+                        'message': _("O produto %s tem peso igual a zero, \
+                            caso não seja alterado, o rateio do frete \
+                            não o considerará.") % (line.product_id.name),
+                    }
+                }
+        if 'warning' in res:
+            return res
+
+    def _calc_percentual_weight(self, line, full_weight):
             if line.product_id.fiscal_type == 'service':
-                continue
+                return
             total_weight = (line.product_id.weight * line.product_qty)
             percentual = total_weight / full_weight
-            line.update({
-                'valor_frete': self.total_frete * percentual
-            })
+            return self.total_frete * percentual
+
+    def _calc_total_weight(self):
+        full_weight = 0
+        for line in self.order_line:
+            if line.product_id.fiscal_type == 'product':
+                full_weight += (line.product_id.weight * line.product_qty)
+        if full_weight == 0 and self.order_line:
+            raise UserError(_("Nenhum dos produtos possui peso cadastrado. \
+                    É necessário corrigir para o calculo do frete."))
+        return full_weight