diff --git a/addons/purchase/models/purchase.py b/addons/purchase/models/purchase.py
index de017ae648a..ed511de6d56 100644
--- a/addons/purchase/models/purchase.py
+++ b/addons/purchase/models/purchase.py
@@ -1231,8 +1231,15 @@ class PurchaseOrderLine(models.Model):
             price_unit = seller.product_uom._compute_price(price_unit, self.product_uom)
 
         self.price_unit = price_unit
-        product_ctx = {'seller_id': seller.id, 'lang': get_lang(self.env, self.partner_id.lang).code}
-        if seller.product_name:
+
+        default_names = []
+        vendors = self.product_id._prepare_sellers({})
+        for vendor in vendors:
+            product_ctx = {'seller_id': vendor.id, 'lang': get_lang(self.env, self.partner_id.lang).code}
+            default_names.append(self._get_product_purchase_description(self.product_id.with_context(product_ctx)))
+
+        if (self.name in default_names or not self.name):
+            product_ctx = {'seller_id': seller.id, 'lang': get_lang(self.env, self.partner_id.lang).code}
             self.name = self._get_product_purchase_description(self.product_id.with_context(product_ctx))
 
     @api.onchange('product_id', 'product_qty', 'product_uom')
diff --git a/addons/purchase/tests/test_purchase.py b/addons/purchase/tests/test_purchase.py
index 983ad102107..1c0267682d2 100644
--- a/addons/purchase/tests/test_purchase.py
+++ b/addons/purchase/tests/test_purchase.py
@@ -248,3 +248,21 @@ class TestPurchase(AccountTestInvoicingCommon):
 
         self.assertEqual(po.order_line[0].price_unit, 200)
         self.assertEqual(po.order_line[1].price_unit, 1200)
+
+    def test_on_change_quantity_description(self):
+        """
+        When a user changes the quantity of a product in a purchase order it
+        should not change the description if the descritpion was changed by
+        the user before
+        """
+        self.env.user.write({'company_id': self.company_data['company'].id})
+
+        po = Form(self.env['purchase.order'])
+        po.partner_id = self.partner_a
+        with po.order_line.new() as pol:
+            pol.product_id = self.product_a
+            pol.product_qty = 1
+
+        pol.name = "New custom description"
+        pol.product_qty += 1
+        self.assertEqual(pol.name, "New custom description")