diff --git a/intrastat_product/models/intrastat_product_declaration.py b/intrastat_product/models/intrastat_product_declaration.py
index a369354..d700233 100644
--- a/intrastat_product/models/intrastat_product_declaration.py
+++ b/intrastat_product/models/intrastat_product_declaration.py
@@ -668,6 +668,51 @@ class IntrastatProductDeclaration(models.Model):
         hashcode = '-'.join([str(f) for f in hc_fields.values()])
         return hashcode
 
+    @api.model
+    def _prepare_grouped_fields(self, computation_line, fields_to_sum):
+        vals = {
+            'src_dest_country_id': computation_line.src_dest_country_id.id,
+            'intrastat_unit_id': computation_line.intrastat_unit_id.id,
+            'hs_code_id': computation_line.hs_code_id.id,
+            'transaction_id': computation_line.transaction_id.id,
+            'transport_id': computation_line.transport_id.id,
+            'region_id': computation_line.region_id.id,
+            'parent_id': computation_line.parent_id.id,
+            'product_origin_country_id':
+            computation_line.product_origin_country_id.id,
+            'amount_company_currency': 0.0,
+            }
+        for field in fields_to_sum:
+            vals[field] = 0.0
+        return vals
+
+    def _fields_to_sum(self):
+        fields_to_sum = [
+            'weight',
+            'suppl_unit_qty',
+            ]
+        return fields_to_sum
+
+    @api.model
+    def _prepare_declaration_line(self, computation_lines):
+        fields_to_sum = self._fields_to_sum()
+        vals = self._prepare_grouped_fields(
+            computation_lines[0], fields_to_sum)
+        for computation_line in computation_lines:
+            for field in fields_to_sum:
+                vals[field] += computation_line[field]
+            vals['amount_company_currency'] += (
+                computation_line['amount_company_currency'] +
+                computation_line['amount_accessory_cost_company_currency'])
+        # round, otherwise odoo with truncate (6.7 -> 6... instead of 7 !)
+        for field in fields_to_sum:
+            vals[field] = int(round(vals[field]))
+        if not vals['weight']:
+            vals['weight'] = 1
+        vals['amount_company_currency'] = int(round(
+            vals['amount_company_currency']))
+        return vals
+
     @api.multi
     def generate_declaration(self):
         """ generate declaration lines """
@@ -686,7 +731,7 @@ class IntrastatProductDeclaration(models.Model):
                 dl_group[hashcode] = [cl]
         ipdl = self.declaration_line_ids
         for cl_lines in list(dl_group.values()):
-            vals = ipdl._prepare_declaration_line(cl_lines)
+            vals = self._prepare_declaration_line(cl_lines)
             declaration_line = ipdl.create(vals)
             for cl in cl_lines:
                 cl.write({'declaration_line_id': declaration_line.id})
@@ -881,6 +926,11 @@ class IntrastatProductDeclarationLine(models.Model):
 
     @api.model
     def _prepare_grouped_fields(self, computation_line, fields_to_sum):
+        """
+        This method is DEPRECATED.
+        You should use the _prepare_grouped_fields method on the
+        IntrastatProductDeclaration class.
+        """
         vals = {
             'src_dest_country_id': computation_line.src_dest_country_id.id,
             'intrastat_unit_id': computation_line.intrastat_unit_id.id,
@@ -898,6 +948,11 @@ class IntrastatProductDeclarationLine(models.Model):
         return vals
 
     def _fields_to_sum(self):
+        """
+        This method is DEPRECATED.
+        You should use the _fields_to_sum method on the
+        IntrastatProductDeclaration class.
+        """
         fields_to_sum = [
             'weight',
             'suppl_unit_qty',
@@ -906,6 +961,11 @@ class IntrastatProductDeclarationLine(models.Model):
 
     @api.model
     def _prepare_declaration_line(self, computation_lines):
+        """
+        This method is DEPRECATED.
+        You should use the _fields_to_sum method on the
+        IntrastatProductDeclaration class.
+        """
         fields_to_sum = self._fields_to_sum()
         vals = self._prepare_grouped_fields(
             computation_lines[0], fields_to_sum)