diff --git a/addons/stock_dropshipping/models/purchase.py b/addons/stock_dropshipping/models/purchase.py
index cefc96ee830..533ecc89187 100644
--- a/addons/stock_dropshipping/models/purchase.py
+++ b/addons/stock_dropshipping/models/purchase.py
@@ -17,7 +17,9 @@ class PurchaseOrderLine(models.Model):
         return res
 
     def _merge_in_existing_line(self, product_id, product_qty, product_uom, location_id, name, origin, values):
-        if values.get('route_ids') and values['route_ids'] == self.env.ref('stock_dropshipping.route_drop_shipping'):
+        if values.get('sale_line_id') and values['sale_line_id'] != self.sale_line_id.id:
+            # if this is defined, this is a dropshipping line, so no
+            # this is to correctly map delivered quantities to the so lines
             return False
         return super(PurchaseOrderLine, self)._merge_in_existing_line(
             product_id=product_id, product_qty=product_qty, product_uom=product_uom,
diff --git a/addons/stock_dropshipping/tests/test_dropship.py b/addons/stock_dropshipping/tests/test_dropship.py
index 7fb7a4ddf7c..5eb9bf8bf57 100644
--- a/addons/stock_dropshipping/tests/test_dropship.py
+++ b/addons/stock_dropshipping/tests/test_dropship.py
@@ -43,3 +43,19 @@ class TestDropship(TransactionCase):
         # Update qty on SO and check PO
         so.order_line.product_uom_qty = 2.00
         self.assertAlmostEqual(po_line.product_qty, 2.00)
+
+        # Create a new so line
+        sol2 = self.env['sale.order.line'].create({
+            'order_id': so.id,
+            'name': prod.name,
+            'product_id': prod.id,
+            'product_uom_qty': 3.00,
+            'product_uom': prod.uom_id.id,
+            'price_unit': 12,
+        })
+        # there is a new line
+        pol2 = po.order_line - po_line
+        # the first line is unchanged
+        self.assertAlmostEqual(po_line.product_qty, 2.00)
+        # the new line matches the new line on the so
+        self.assertAlmostEqual(pol2.product_qty, sol2.product_uom_qty)