diff --git a/addons/stock/models/stock_quant.py b/addons/stock/models/stock_quant.py
index 84e7b5596dd..ac1a814636d 100644
--- a/addons/stock/models/stock_quant.py
+++ b/addons/stock/models/stock_quant.py
@@ -917,7 +917,7 @@ class StockQuant(models.Model):
                 self.product_id, self.location_id, lot_id=self.lot_id,
                 package_id=self.package_id, owner_id=self.owner_id, strict=True)
             if quant:
-                self.quantity = quant.filtered(lambda q: q.lot_id == self.lot_id).quantity
+                self.quantity = sum(quant.filtered(lambda q: q.lot_id == self.lot_id).mapped('quantity'))
 
             # Special case: directly set the quantity to one for serial numbers,
             # it'll trigger `inventory_quantity` compute.