diff --git a/addons/mrp/models/stock_move.py b/addons/mrp/models/stock_move.py
index 5cb92a5025c..2017b5d9490 100644
--- a/addons/mrp/models/stock_move.py
+++ b/addons/mrp/models/stock_move.py
@@ -33,7 +33,7 @@ class StockMoveLots(models.Model):
     def _check_lot_id(self):
         if self.move_id.product_id.tracking == 'serial':
             lots = set([])
-            for move_lot in self.move_id.move_lot_ids.filtered(lambda r: not r.lot_produced_id):
+            for move_lot in self.move_id.move_lot_ids.filtered(lambda r: not r.lot_produced_id and r.lot_id):
                 if move_lot.lot_id in lots:
                     raise exceptions.UserError(_('You cannot use the same serial number in two different lines.'))
                 if float_compare(move_lot.quantity_done, 1.0, precision_rounding=move_lot.product_id.uom_id.rounding) == 1: