diff --git a/addons/sale/models/account_move.py b/addons/sale/models/account_move.py
index 0087647235a..11a46e3eb45 100644
--- a/addons/sale/models/account_move.py
+++ b/addons/sale/models/account_move.py
@@ -150,17 +150,19 @@ class AccountMove(models.Model):
     def _compute_partner_credit(self):
         super()._compute_partner_credit()
         for move in self:
-            sale_order = move.line_ids.sale_line_ids.order_id
+            sale_orders = move.line_ids.sale_line_ids.order_id
             amount_total_currency = move.currency_id._convert(
                 move.tax_totals['amount_total'],
                 move.company_currency_id,
                 move.company_id,
                 move.date
             )
-            amount_to_invoice_currency = sale_order.currency_id._convert(
-                sale_order.amount_to_invoice,
-                move.company_currency_id,
-                move.company_id,
-                move.date
+            amount_to_invoice_currency = sum(
+                sale_order.currency_id._convert(
+                    sale_order.amount_to_invoice,
+                    move.company_currency_id,
+                    move.company_id,
+                    move.date
+                ) for sale_order in sale_orders
             )
             move.partner_credit += max(amount_total_currency - amount_to_invoice_currency, 0.0)