diff --git a/modules/purchase_trade/sale.py b/modules/purchase_trade/sale.py
index 803250d..e70b6db 100755
--- a/modules/purchase_trade/sale.py
+++ b/modules/purchase_trade/sale.py
@@ -1062,7 +1062,7 @@ class SaleLine(metaclass=PoolMeta):
                 continue
             quantity = Decimal(str(invoice_line.quantity or 0)) + padding
             if invoice_line.unit:
-                quantity = Decimal(str(invoice_line.unit.round(quantity)))
+                quantity = Decimal(str(invoice_line.unit.round(float(quantity))))
             invoice_line.quantity = quantity
         return lines