diff --git a/account_invoice_fiscal_position_update/models/account_move.py b/account_invoice_fiscal_position_update/models/account_move.py
index 2ce654d8a7c..9c6b736a8f0 100644
--- a/account_invoice_fiscal_position_update/models/account_move.py
+++ b/account_invoice_fiscal_position_update/models/account_move.py
@@ -40,5 +40,5 @@ def _onchange_fiscal_position_id_account_invoice_fiscal_position_invoice(self):
                     "to the new Fiscal Position because they don't have a "
                     "Product:\n - %s\nYou should update the Account and the "
                     "Taxes of these invoice lines manually."
-                ) % ("\n- ".join(lines_without_product.mapped("name")))
+                ) % ("\n- ".join([str(k.name) for k in lines_without_product]))
         return res