diff --git a/addons/sale/models/res_partner.py b/addons/sale/models/res_partner.py
index 0ac1409cd00..05d3f21f05f 100644
--- a/addons/sale/models/res_partner.py
+++ b/addons/sale/models/res_partner.py
@@ -14,11 +14,17 @@ class ResPartner(models.Model):
     sale_warn_msg = fields.Text('Message for Sales Order')
 
     def _compute_sale_order_count(self):
-        sale_data = self.env['sale.order'].read_group(domain=[('partner_id', 'child_of', self.ids)],
-                                                      fields=['partner_id'], groupby=['partner_id'])
-        mapped_data = dict([(m['partner_id'][0], m['partner_id_count']) for m in sale_data])
-        for partner in self:
-            # let's obtain the partner id and all its child ids
-            partner_ids = [partner.id] + partner.child_ids.ids
-            # then we can sum for all the partner's child
-            partner.sale_order_count = sum(mapped_data.get(child, 0) for child in partner_ids)
+        # retrieve all children partners and prefetch 'parent_id' on them
+        all_partners = self.search([('id', 'child_of', self.ids)])
+        all_partners.read(['parent_id'])
+
+        sale_order_groups = self.env['sale.order'].read_group(
+            domain=[('partner_id', 'in', all_partners.ids)],
+            fields=['partner_id'], groupby=['partner_id']
+        )
+        for group in sale_order_groups:
+            partner = self.browse(group['partner_id'][0])
+            while partner:
+                if partner in self:
+                    partner.sale_order_count += group['partner_id_count']
+                partner = partner.parent_id