diff --git a/product_category_tax/product.py b/product_category_tax/product.py
index 141f29e..4606546 100644
--- a/product_category_tax/product.py
+++ b/product_category_tax/product.py
@@ -24,19 +24,48 @@ from openerp import models, fields, api, _
 from openerp.exceptions import ValidationError
 
 
-class ProductTemplate(models.Model):
-    _inherit = 'product.template'
+class ProductCategTaxMixin(models.AbstractModel):
+    _name = 'product.categ.tax.mixin'
 
     @api.onchange('categ_id')
     def onchange_categ_id(self):
         if self.categ_id:
-            # I cannot use the commented line below:
-            #self.taxes_id = self.categ_id.sale_tax_ids.ids
-            # because it ADDS the taxes (equivalent of (4, ID)) instead
-            # of replacing the taxes... and I want to REPLACE the taxes
-            # So I have to use the awful syntax (6, 0, [IDs])
-            self.taxes_id = [(6, 0, self.categ_id.sale_tax_ids.ids)]
-            self.supplier_taxes_id = [(6, 0, self.categ_id.purchase_tax_ids.ids)]
+            self.taxes_id, self.supplier_taxes_id = (
+                self.apply_tax_from_category(self.categ_id))
+
+    @api.model
+    def apply_tax_from_category(self, categ_id):
+        # self.ensure_one()
+        #   I cannot use the commented line below:
+        # self.taxes_id = self.categ_id.sale_tax_ids.ids
+        #   because it ADDS the taxes (equivalent of (4, ID)) instead
+        #   of replacing the taxes... and I want to REPLACE the taxes
+        #   So I have to use the awful syntax (6, 0, [IDs])
+        # values are sent to ('taxes_id' and 'supplier_taxes_id')
+        return ([(6, 0, categ_id.sale_tax_ids.ids)],
+                [(6, 0, categ_id.purchase_tax_ids.ids)])
+
+    @api.model
+    def write_or_create(self, vals):
+        if vals.get('categ_id'):
+            vals['taxes_id'], vals['supplier_taxes_id'] = (
+                self.apply_tax_from_category(
+                    self.categ_id.browse(vals['categ_id'])))
+
+    @api.model
+    def create(self, vals):
+        self.write_or_create(vals)
+        return super(ProductCategTaxMixin, self).create(vals)
+
+    @api.multi
+    def write(self, vals):
+        self.write_or_create(vals)
+        return super(ProductCategTaxMixin, self).create(vals)
+
+
+class ProductTemplate(models.Model):
+    _inherit = ['product.template', 'product.categ.tax.mixin']
+    _name = 'product.template'
 
     @api.one
     @api.constrains('taxes_id', 'supplier_taxes_id')
@@ -61,13 +90,8 @@ class ProductTemplate(models.Model):
 
 
 class ProductProduct(models.Model):
-    _inherit = 'product.product'
-
-    @api.onchange('categ_id')
-    def onchange_categ_id(self):
-        if self.categ_id:
-            self.taxes_id = [(6, 0, self.categ_id.sale_tax_ids.ids)]
-            self.supplier_taxes_id = [(6, 0, self.categ_id.purchase_tax_ids.ids)]
+    _inherit = ['product.product', 'product.categ.tax.mixin']
+    _name = 'product.product'
 
 
 class ProductCategory(models.Model):