diff --git a/account_invoice_triple_discount/models/account_move.py b/account_invoice_triple_discount/models/account_move.py
index 20042c73161..9f7c54a6d97 100644
--- a/account_invoice_triple_discount/models/account_move.py
+++ b/account_invoice_triple_discount/models/account_move.py
@@ -16,9 +16,10 @@ def _recompute_tax_lines(self, **kwargs):
         restored after the original process is done
         """
         old_values_by_line_id = {}
-        digits = self.invoice_line_ids._fields["price_unit"]._digits
-        self.invoice_line_ids._fields["price_unit"]._digits = (16, 16)
-        for line in self.invoice_line_ids:
+        lines = self.invoice_line_ids or self.line_ids
+        digits = lines._fields["price_unit"]._digits
+        lines._fields["price_unit"]._digits = (16, 16)
+        for line in lines:
             aggregated_discount = line._compute_aggregated_discount(line.discount)
             old_values_by_line_id[line.id] = {
                 "price_unit": line.price_unit,
@@ -26,9 +27,9 @@ def _recompute_tax_lines(self, **kwargs):
             }
             price_unit = line.price_unit * (1 - aggregated_discount / 100)
             line.update({"price_unit": price_unit, "discount": 0})
-        self.invoice_line_ids._fields["price_unit"]._digits = digits
+        lines._fields["price_unit"]._digits = digits
         res = super(AccountMove, self)._recompute_tax_lines(**kwargs)
-        for line in self.invoice_line_ids:
+        for line in lines:
             if line.id not in old_values_by_line_id:
                 continue
             line.update(old_values_by_line_id[line.id])
@@ -36,9 +37,7 @@ def _recompute_tax_lines(self, **kwargs):
 
     def _has_discount(self):
         self.ensure_one()
+        lines = self.invoice_line_ids or self.line_ids
         return any(
-            [
-                line._compute_aggregated_discount(line.discount) > 0
-                for line in self.invoice_line_ids
-            ]
+            [line._compute_aggregated_discount(line.discount) > 0 for line in lines]
         )