diff --git a/addons/sale_purchase/models/sale_order.py b/addons/sale_purchase/models/sale_order.py
index 46a43535e88..cc98322055e 100644
--- a/addons/sale_purchase/models/sale_order.py
+++ b/addons/sale_purchase/models/sale_order.py
@@ -19,7 +19,7 @@ class SaleOrder(models.Model):
     @api.depends('order_line.purchase_line_ids.order_id')
     def _compute_purchase_order_count(self):
         for order in self:
-            order.purchase_order_count = len(self._get_purchase_orders())
+            order.purchase_order_count = len(order._get_purchase_orders())
 
     def _action_confirm(self):
         result = super(SaleOrder, self)._action_confirm()