diff --git a/addons/sale/models/account_move.py b/addons/sale/models/account_move.py
index ca040c8c92f..48faa9306b1 100644
--- a/addons/sale/models/account_move.py
+++ b/addons/sale/models/account_move.py
@@ -59,20 +59,21 @@ class AccountMove(models.Model):
         return super()._reverse_moves(default_values_list=default_values_list, cancel=cancel)
 
     def action_post(self):
-        #inherit of the function from account.move to validate a new tax and the priceunit of a downpayment
+        # inherit of the function from account.move to validate a new tax and the priceunit of a downpayment
         res = super(AccountMove, self).action_post()
-        down_payment_lines = self.line_ids.filtered('is_downpayment')
-        for line in down_payment_lines:
-            if not any(sol.display_type for sol in line.sale_line_ids):
-                line.sale_line_ids._compute_name()
 
-            if any(order.locked for order in line.sale_line_ids.order_id):
-                # We cannot change lines content on locked SO, changes on invoices are not
-                # forwarded to the SO if the SO is locked.
-                continue
+        # We cannot change lines content on locked SO, changes on invoices are not forwarded to the SO if the SO is locked
+        downpayment_lines = self.line_ids.sale_line_ids.filtered(lambda l: l.is_downpayment and not l.display_type and not l.order_id.locked)
+        other_so_lines = downpayment_lines.order_id.order_line - downpayment_lines
+        real_invoices = set(other_so_lines.invoice_lines.move_id)
+        for so_dpl in downpayment_lines:
+            so_dpl.price_unit = sum(
+                l.price_unit if l.move_id.move_type == 'out_invoice' else -l.price_unit
+                for l in so_dpl.invoice_lines
+                if l.move_id.state == 'posted' and l.move_id not in real_invoices  # don't recompute with the final invoice
+            )
+            so_dpl.tax_id = so_dpl.invoice_lines.tax_ids
 
-            line.sale_line_ids.tax_id = line.tax_ids
-            line.sale_line_ids.price_unit = line.price_unit
         return res
 
     def button_draft(self):
diff --git a/addons/sale/tests/test_sale_to_invoice.py b/addons/sale/tests/test_sale_to_invoice.py
index b1cf0b04ee2..bc881ad2da1 100644
--- a/addons/sale/tests/test_sale_to_invoice.py
+++ b/addons/sale/tests/test_sale_to_invoice.py
@@ -186,16 +186,17 @@ class TestSaleToInvoice(TestSaleCommon):
             'deposit_account_id': self.company_data['default_account_revenue'].id
         })
         downpayment.create_invoices()
-        # Let's do the invoice
+        # Let's do the invoice for the remaining amount
         payment = self.env['sale.advance.payment.inv'].with_context(context).create({
             'deposit_account_id': self.company_data['default_account_revenue'].id
         })
         payment.create_invoices()
-        # Confirm all invoices
-        for invoice in sale_order.invoice_ids:
-            invoice.action_post()
+
         downpayment_line = sale_order.order_line.filtered(lambda l: l.is_downpayment and not l.display_type)
         self.assertEqual(downpayment_line[0].price_unit, 50, 'The down payment unit price should not change on SO')
+        # Confirm all invoices
+        sale_order.invoice_ids.action_post()
+        self.assertEqual(downpayment_line[0].price_unit, 50, 'The down payment unit price should not change on SO')
 
     def test_downpayment_fixed_amount_with_zero_total_amount(self):
         # Create the SO with one line and amount total is zero
@@ -261,6 +262,46 @@ class TestSaleToInvoice(TestSaleCommon):
         invoice.action_post()
         self.assertEqual(downpayment_line.price_unit, self.sale_order.amount_total/2, 'downpayment should have the correct amount')
 
+    def test_downpayment_invoice_and_partial_credit_note(self):
+        """This test check that the downpayment line amount on the sale order remains consistent"""
+        self.sale_order.action_confirm()
+
+        # Create an invoice for a Down payment of 100
+        payment = self.env['sale.advance.payment.inv'].with_context(self.context).create({
+            'advance_payment_method': 'fixed',
+            'fixed_amount': 100,
+            'deposit_account_id': self.company_data['default_account_revenue'].id,
+        })
+        payment.create_invoices()
+
+        # Ensure the downpayment line on the sale order is correctly set to 100
+        downpayment_line = self.sale_order.order_line.filtered(lambda l: l.is_downpayment and not l.display_type)
+        self.assertEqual(downpayment_line.price_unit, 100)
+
+        # post the downpayment invoice and ensure the downpayment_line amount is still 100
+        downpayment_invoice = downpayment_line.order_id.order_line.invoice_lines.move_id
+        downpayment_invoice.action_post()
+        self.assertEqual(downpayment_line.price_unit, 100)
+
+        # Create a credit note for a part of the downpayment invoice and post it
+        move_reversal = self.env['account.move.reversal'].with_context(
+            active_model="account.move",
+            active_ids=downpayment_invoice.ids,
+        ).create({
+            'date': '2020-02-01',
+            'reason': 'no reason',
+            'journal_id': downpayment_invoice.journal_id.id,
+        })
+        reversal_action = move_reversal.reverse_moves()
+        reverse_move = self.env['account.move'].browse(reversal_action['res_id'])
+        with Form(reverse_move) as form_reverse:
+            with form_reverse.invoice_line_ids.edit(0) as line_form:
+                line_form.price_unit = 20.0
+        reverse_move.action_post()
+
+        self.assertEqual(downpayment_line.price_unit, 80,
+                         "The downpayment line amount should be equal to the sum of the invoice and credit note amount")
+
     def test_invoice_with_discount(self):
         """ Test invoice with a discount and check discount applied on both SO lines and an invoice lines """
         # Update discount and delivered quantity on SO lines