diff --git a/addons/purchase/purchase.py b/addons/purchase/purchase.py
index 8f01ecce86f..6a6a329ee15 100644
--- a/addons/purchase/purchase.py
+++ b/addons/purchase/purchase.py
@@ -571,8 +571,8 @@ class PurchaseOrderLine(models.Model):
         if price_unit and seller and self.order_id.currency_id and seller.currency_id != self.order_id.currency_id:
             price_unit = seller.currency_id.compute(price_unit, self.order_id.currency_id)
         self.price_unit = price_unit
-
-        self.date_planned = self._get_date_planned(seller).strftime(DEFAULT_SERVER_DATETIME_FORMAT)
+        if seller or not self.date_planned:
+            self.date_planned = self._get_date_planned(seller).strftime(DEFAULT_SERVER_DATETIME_FORMAT)
 
         product_lang = self.product_id.with_context({
             'lang': self.partner_id.lang,