diff --git a/sale.py b/sale.py
index 44676809c5..f19dcec701 100644
--- a/sale.py
+++ b/sale.py
@@ -1165,8 +1165,9 @@ class SaleLine(ModelSQL, ModelView):
         ignored_ids = set(
             l.id for i in line.sale.invoices_ignored for l in i.lines)
         for invoice_line in line.invoice_lines:
-            if invoice_line.invoice.state != 'cancel' or \
-                    invoice_line.id in ignored_ids:
+            if ((invoice_lines.invoice and
+                    invoice_line.invoice.state != 'cancel') or
+                invoice_line.id in ignored_ids):
                 quantity -= uom_obj.compute_qty(invoice_line.unit, 
                         invoice_line.quantity, line.unit)
         res['quantity'] = quantity