diff --git a/modules/purchase_trade/lot.py b/modules/purchase_trade/lot.py
index 56acd7e..efb5f9f 100755
--- a/modules/purchase_trade/lot.py
+++ b/modules/purchase_trade/lot.py
@@ -2693,7 +2693,7 @@ class LotInvoice(Wizard):
                 val_s['lot_diff_price'] = val_s['lot_price'] - Decimal(lot.sale_invoice_line_prov.unit_price)
                 val_s['lot_diff_amount'] = val_s['lot_amount'] - Decimal(lot.sale_invoice_line_prov.amount)
             val_s['lot_currency'] = lot.lot_price_ct_symbol_sale
-            val_s['lot_unit'] = sale_line.unit if sale_line else None
+            val_s['lot_unit'] = sale_line.unit.id if sale_line else None
             lot_s.append(val_s)
         if line:
             if line.fees: