diff --git a/account_invoice_fixed_discount/__manifest__.py b/account_invoice_fixed_discount/__manifest__.py
index a278b84b6d75..eb784cdb397e 100644
--- a/account_invoice_fixed_discount/__manifest__.py
+++ b/account_invoice_fixed_discount/__manifest__.py
@@ -4,7 +4,7 @@
 {
     "name": "Account Fixed Discount",
     "summary": "Allows to apply fixed amount discounts in invoices.",
-    "version": "15.0.1.0.0",
+    "version": "16.0.1.0.0",
     "category": "Accounting & Finance",
     "website": "https://github.com/OCA/account-invoicing",
     "author": "ForgeFlow, Odoo Community Association (OCA)",
@@ -12,5 +12,9 @@
     "application": False,
     "installable": True,
     "depends": ["account"],
-    "data": ["views/account_move_view.xml", "reports/report_account_invoice.xml"],
+    "data": [
+        "security/res_groups.xml",
+        "views/account_move_view.xml",
+        "reports/report_account_invoice.xml",
+    ],
 }
diff --git a/account_invoice_fixed_discount/models/__init__.py b/account_invoice_fixed_discount/models/__init__.py
index 44b2c7a5e83a..cc589d1c321e 100644
--- a/account_invoice_fixed_discount/models/__init__.py
+++ b/account_invoice_fixed_discount/models/__init__.py
@@ -1,3 +1,3 @@
 # License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl)
 
-from . import account_move
+from . import account_move_line
diff --git a/account_invoice_fixed_discount/models/account_move.py b/account_invoice_fixed_discount/models/account_move.py
deleted file mode 100644
index 553223ccdff5..000000000000
--- a/account_invoice_fixed_discount/models/account_move.py
+++ /dev/null
@@ -1,124 +0,0 @@
-# Copyright 2017 ForgeFlow S.L.
-# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl)
-
-from odoo import _, api, fields, models
-from odoo.exceptions import ValidationError
-
-
-class AccountMove(models.Model):
-    _inherit = "account.move"
-
-    def _recompute_tax_lines(
-        self, recompute_tax_base_amount=False, tax_rep_lines_to_recompute=None
-    ):
-        vals = {}
-        for line in self.invoice_line_ids.filtered("discount_fixed"):
-            vals[line] = {"price_unit": line.price_unit}
-            price_unit = line.price_unit - line.discount_fixed
-            line.update({"price_unit": price_unit})
-        res = super(AccountMove, self)._recompute_tax_lines(
-            recompute_tax_base_amount=recompute_tax_base_amount,
-            tax_rep_lines_to_recompute=tax_rep_lines_to_recompute,
-        )
-        for line in vals.keys():
-            line.update(vals[line])
-        return res
-
-
-class AccountMoveLine(models.Model):
-    _inherit = "account.move.line"
-
-    discount_fixed = fields.Float(
-        string="Discount (Fixed)",
-        digits="Product Price",
-        default=0.00,
-        help="Fixed amount discount.",
-    )
-
-    @api.onchange("discount")
-    def _onchange_discount(self):
-        if self.discount:
-            self.discount_fixed = 0.0
-
-    @api.onchange("discount_fixed")
-    def _onchange_discount_fixed(self):
-        if self.discount_fixed:
-            self.discount = 0.0
-
-    @api.constrains("discount", "discount_fixed")
-    def _check_only_one_discount(self):
-        for rec in self:
-            for line in rec:
-                if line.discount and line.discount_fixed:
-                    raise ValidationError(
-                        _("You can only set one type of discount per line.")
-                    )
-
-    @api.onchange("quantity", "discount", "price_unit", "tax_ids", "discount_fixed")
-    def _onchange_price_subtotal(self):
-        return super(AccountMoveLine, self)._onchange_price_subtotal()
-
-    @api.model
-    def _get_price_total_and_subtotal_model(
-        self,
-        price_unit,
-        quantity,
-        discount,
-        currency,
-        product,
-        partner,
-        taxes,
-        move_type,
-    ):
-        if self.discount_fixed != 0:
-            discount = ((self.discount_fixed) / price_unit) * 100 or 0.00
-        return super(AccountMoveLine, self)._get_price_total_and_subtotal_model(
-            price_unit, quantity, discount, currency, product, partner, taxes, move_type
-        )
-
-    @api.model
-    def _get_fields_onchange_balance_model(
-        self,
-        quantity,
-        discount,
-        amount_currency,
-        move_type,
-        currency,
-        taxes,
-        price_subtotal,
-        force_computation=False,
-    ):
-        if self.discount_fixed != 0:
-            discount = ((self.discount_fixed) / self.price_unit) * 100 or 0.00
-        return super(AccountMoveLine, self)._get_fields_onchange_balance_model(
-            quantity,
-            discount,
-            amount_currency,
-            move_type,
-            currency,
-            taxes,
-            price_subtotal,
-            force_computation=force_computation,
-        )
-
-    @api.model_create_multi
-    def create(self, vals_list):
-        prev_discount = []
-        for vals in vals_list:
-            if vals.get("discount_fixed"):
-                prev_discount.append(
-                    {"discount_fixed": vals.get("discount_fixed"), "discount": 0.00}
-                )
-                fixed_discount = (
-                    vals.get("discount_fixed") / vals.get("price_unit")
-                ) * 100
-                vals.update({"discount": fixed_discount, "discount_fixed": 0.00})
-            elif vals.get("discount"):
-                prev_discount.append({"discount": vals.get("discount")})
-        res = super(AccountMoveLine, self).create(vals_list)
-        i = 0
-        for rec in res:
-            if rec.discount and prev_discount:
-                rec.write(prev_discount[i])
-                i += 1
-        return res
diff --git a/account_invoice_fixed_discount/models/account_move_line.py b/account_invoice_fixed_discount/models/account_move_line.py
new file mode 100644
index 000000000000..6a80a5b5dcdf
--- /dev/null
+++ b/account_invoice_fixed_discount/models/account_move_line.py
@@ -0,0 +1,66 @@
+# Copyright 2017 ForgeFlow S.L.
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl)
+
+from odoo import _, api, fields, models
+from odoo.exceptions import ValidationError
+from odoo.tools.float_utils import float_round
+
+
+class AccountMoveLine(models.Model):
+    _inherit = "account.move.line"
+
+    discount_fixed = fields.Monetary(
+        string="Discount (Fixed)",
+        default=0.0,
+        currency_field="currency_id",
+        help=(
+            "Apply a fixed amount discount to this line. The amount is multiplied by "
+            "the quantity of the product."
+        ),
+    )
+
+    @api.constrains("discount_fixed", "discount")
+    def _check_discounts(self):
+        """Check that the fixed discount and the discount percentage are consistent."""
+        for line in self:
+            if line.discount_fixed and line.discount:
+                currency = line.currency_id
+                calculated_fixed_discount = float_round(
+                    line._get_discount_from_fixed_discount(),
+                    precision_rounding=currency.rounding,
+                )
+
+                if calculated_fixed_discount != line.discount:
+                    raise ValidationError(
+                        _(
+                            "The fixed discount %(fixed)s does not match the calculated "
+                            "discount %(discount)s %%. Please correct one of the discounts."
+                        )
+                        % {
+                            "fixed": line.discount_fixed,
+                            "discount": line.discount,
+                        }
+                    )
+
+    def _get_discount_from_fixed_discount(self):
+        """Calculate the discount percentage from the fixed discount amount."""
+        self.ensure_one()
+        if not self.discount_fixed:
+            return 0.0
+
+        return self.discount_fixed / self.price_unit * 100
+
+    @api.onchange("discount_fixed", "quantity", "price_unit")
+    def _onchange_discount_fixed(self):
+        """When the discount fixed is changed, we set the ``discount`` on the line to the
+        appropriate value and apply the default downstream implementation.
+
+        When the display_type is not ``'product'`` we reset the discount_fixed to 0.0.
+
+        """
+        if self.display_type != "product" or not self.quantity or not self.price_unit:
+            self.discount_fixed = 0.0
+            return
+
+        if self.discount_fixed:
+            self.discount = self._get_discount_from_fixed_discount()
diff --git a/account_invoice_fixed_discount/readme/CONTRIBUTORS.rst b/account_invoice_fixed_discount/readme/CONTRIBUTORS.rst
index ec50e28845c7..44ef0c418c59 100644
--- a/account_invoice_fixed_discount/readme/CONTRIBUTORS.rst
+++ b/account_invoice_fixed_discount/readme/CONTRIBUTORS.rst
@@ -2,3 +2,4 @@
 * Jordi Ballester <jordi.ballester@forgeflow.com>
 * Rattapong Chokmasermkul <rattapongc@ecosoft.co.th>
 * Kitti U. <kittiu@ecosoft.co.th>
+* Pieter Paulussen <pieterpaulussen@code-source.be>
diff --git a/account_invoice_fixed_discount/readme/ROADMAP.rst b/account_invoice_fixed_discount/readme/ROADMAP.rst
deleted file mode 100644
index e1bf21e7ffa6..000000000000
--- a/account_invoice_fixed_discount/readme/ROADMAP.rst
+++ /dev/null
@@ -1,2 +0,0 @@
-* At the moment, the simultaneous use of percent and fixed discounts (at
-  line level) is not supported.
diff --git a/account_invoice_fixed_discount/reports/report_account_invoice.xml b/account_invoice_fixed_discount/reports/report_account_invoice.xml
index ca41330c4f9e..bfd66c8e42ec 100644
--- a/account_invoice_fixed_discount/reports/report_account_invoice.xml
+++ b/account_invoice_fixed_discount/reports/report_account_invoice.xml
@@ -8,18 +8,18 @@
                 t-value="any([l.discount_fixed for l in o.invoice_line_ids])"
             />
         </xpath>
-        <xpath expr="//th[@t-if='display_discount']" position="after">
+        <xpath expr="//th[@t-if='display_discount']" position="before">
             <th
                 t-if="display_discount_fixed"
-                t-attf-class="text-right {{ 'd-none d-md-table-cell' if report_type == 'html' else '' }}"
+                t-attf-class="text-end {{ 'd-none d-md-table-cell' if report_type == 'html' else '' }}"
             >
                 <span>Disc. Fixed Amount</span>
             </th>
         </xpath>
-        <xpath expr="//td[@t-if='display_discount']" position="after">
+        <xpath expr="//td[@t-if='display_discount']" position="before">
             <td
                 t-if="display_discount_fixed"
-                t-attf-class="text-right {{ 'd-none d-md-table-cell' if report_type == 'html' else '' }}"
+                t-attf-class="text-end {{ 'd-none d-md-table-cell' if report_type == 'html' else '' }}"
             >
                 <span t-field="line.discount_fixed" />
             </td>
diff --git a/account_invoice_fixed_discount/security/res_groups.xml b/account_invoice_fixed_discount/security/res_groups.xml
new file mode 100644
index 000000000000..5b6ef73f5946
--- /dev/null
+++ b/account_invoice_fixed_discount/security/res_groups.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<odoo>
+    <data>
+
+        <record id="group_fixed_discount" model="res.groups">
+            <field name="name">Fixed Discount</field>
+        </record>
+
+    </data>
+
+    <data noupdate="1">
+        <record id="account.group_account_invoice" model="res.groups">
+            <field
+                name="implied_ids"
+                eval="[(4, ref('account_invoice_fixed_discount.group_fixed_discount'))]"
+            />
+        </record>
+    </data>
+
+
+</odoo>
diff --git a/account_invoice_fixed_discount/tests/test_account_fixed_discount.py b/account_invoice_fixed_discount/tests/test_account_fixed_discount.py
index 12f690ed9e17..bd3e4ea0ecb0 100644
--- a/account_invoice_fixed_discount/tests/test_account_fixed_discount.py
+++ b/account_invoice_fixed_discount/tests/test_account_fixed_discount.py
@@ -3,29 +3,23 @@
 
 from odoo.exceptions import ValidationError
 from odoo.tests import TransactionCase
+from odoo.tests.common import Form
 
 
 class TestInvoiceFixedDiscount(TransactionCase):
     @classmethod
     def setUpClass(cls):
         super(TestInvoiceFixedDiscount, cls).setUpClass()
+
+        cls.env.user.groups_id |= cls.env.ref("account.group_account_invoice")
         cls.partner = cls.env["res.partner"].create({"name": "Test"})
         cls.product = cls.env.ref("product.product_product_3")
         cls.account = cls.env["account.account"].search(
-            [
-                (
-                    "user_type_id",
-                    "=",
-                    cls.env.ref("account.data_account_type_revenue").id,
-                )
-            ],
+            [("account_type", "=", "income")],
             limit=1,
         )
-        type_current_liability = cls.env.ref(
-            "account.data_account_type_current_liabilities"
-        )
         cls.output_vat_acct = cls.env["account.account"].create(
-            {"name": "10", "code": "10", "user_type_id": type_current_liability.id}
+            {"name": "10", "code": "10", "account_type": "liability_current"}
         )
         cls.tax_group_vat = cls.env["account.tax.group"].create({"name": "VAT"})
         cls.vat = cls.env["account.tax"].create(
@@ -50,33 +44,35 @@ def setUpClass(cls):
                 ],
             }
         )
+        cls.invoice = cls._create_invoice()
 
-    def _create_invoice(self, discount=0.00, discount_fixed=0.00):
+    @classmethod
+    def _create_invoice(cls, discount=0.00, discount_fixed=0.00):
         invoice_vals = [
             (
                 0,
                 0,
                 {
-                    "product_id": self.product.id,
+                    "product_id": cls.product.id,
                     "quantity": 1.0,
-                    "account_id": self.account.id,
+                    "account_id": cls.account.id,
                     "name": "Line 1",
                     "price_unit": 200.00,
                     "discount_fixed": discount_fixed,
                     "discount": discount,
-                    "tax_ids": [(6, 0, [self.vat.id])],
+                    "tax_ids": [(6, 0, [cls.vat.id])],
                 },
             )
         ]
         invoice = (
-            self.env["account.move"]
+            cls.env["account.move"]
             .with_context(check_move_validity=False)
             .create(
                 {
-                    "journal_id": self.env["account.journal"]
+                    "journal_id": cls.env["account.journal"]
                     .search([("type", "=", "sale")], limit=1)
                     .id,
-                    "partner_id": self.partner.id,
+                    "partner_id": cls.partner.id,
                     "move_type": "out_invoice",
                     "invoice_line_ids": invoice_vals,
                 }
@@ -84,24 +80,52 @@ def _create_invoice(self, discount=0.00, discount_fixed=0.00):
         )
         return invoice
 
-    def test_01_discounts_fixed(self):
+    def test_01_discounts_fixed_single_unit(self):
         """Tests multiple discounts in line with taxes."""
-        invoice = self._create_invoice(discount_fixed=57)
-        with self.assertRaises(ValidationError):
-            invoice.invoice_line_ids.discount = 50
-        invoice.invoice_line_ids._onchange_discount_fixed()
-        self.assertEqual(invoice.invoice_line_ids.discount, 0.00)
-        invoice.invoice_line_ids._onchange_price_subtotal()
-        invoice.line_ids.write({"recompute_tax_line": True})
-        invoice._onchange_invoice_line_ids()
+
+        # Fixed discount 1.0 unit at 57.00
+        with Form(self.invoice) as invoice_form:
+            with invoice_form.invoice_line_ids.edit(0) as line:
+                line.discount_fixed = 57.00
+
+        # compute discount (57 / 200) * 100
+        self.assertEqual(self.invoice.invoice_line_ids.discount, 28.5)
         # compute amount total (200 - 57) * 10%
-        self.assertEqual(invoice.amount_total, 157.3)
-        self.assertEqual(invoice.invoice_line_ids.price_unit, 200.00)
-        self.assertEqual(invoice.invoice_line_ids.price_subtotal, 143.00)
+        self.assertEqual(self.invoice.amount_total, 157.3)
+        self.assertEqual(self.invoice.invoice_line_ids.price_unit, 200.00)
+        self.assertEqual(self.invoice.invoice_line_ids.price_subtotal, 143.00)
+
+        # Reset to regular discount at 20.00%
+        with Form(self.invoice) as invoice_form:
+            with invoice_form.invoice_line_ids.edit(0) as line:
+                line.discount_fixed = 0
+                line.discount = 20.0
+
+        self.assertEqual(self.invoice.amount_total, 176.0)
+        self.assertEqual(self.invoice.invoice_line_ids.price_unit, 200.00)
+        self.assertEqual(self.invoice.invoice_line_ids.price_subtotal, 160.00)
+
+    def test_02_discounts_fixed_multiple_units(self):
+        """Tests multiple discounts in line with taxes."""
+
+        # Fixed discount 2.0 units at 50.00
+        with Form(self.invoice) as invoice_form:
+            with invoice_form.invoice_line_ids.edit(0) as line:
+                line.discount_fixed = 25.00
+                line.quantity = 2.0
+
+        # compute discount ((50 / 2) / 200) * 100
+        self.assertEqual(self.invoice.invoice_line_ids.discount, 12.5)
+        self.assertEqual(self.invoice.amount_total, 385.0)
+        self.assertEqual(self.invoice.invoice_line_ids.price_unit, 200.00)
+        self.assertEqual(self.invoice.invoice_line_ids.price_subtotal, 350)
+
+    def test_03_discount_validation(self):
 
-    def test_02_discounts(self):
-        invoice = self._create_invoice(discount=50)
-        invoice.invoice_line_ids._onchange_discount()
-        self.assertEqual(invoice.invoice_line_ids.discount_fixed, 0.00)
-        self.assertEqual(invoice.invoice_line_ids.price_unit, 200.00)
-        self.assertEqual(invoice.invoice_line_ids.price_subtotal, 100.00)
+        with self.assertRaisesRegex(
+            ValidationError, "Please correct one of the discounts"
+        ):
+            with Form(self.invoice) as invoice_form:
+                with invoice_form.invoice_line_ids.edit(0) as line:
+                    line.discount_fixed = 57.00
+                    line.discount = 20.0
diff --git a/account_invoice_fixed_discount/views/account_move_view.xml b/account_invoice_fixed_discount/views/account_move_view.xml
index c54fc7bca06d..a6fd476a5011 100644
--- a/account_invoice_fixed_discount/views/account_move_view.xml
+++ b/account_invoice_fixed_discount/views/account_move_view.xml
@@ -12,21 +12,20 @@
             >
                 <field
                     name="discount_fixed"
-                    groups="base.group_no_one"
+                    groups="account_invoice_fixed_discount.group_fixed_discount"
                     optional="show"
+                    context="{'ignore_discount_fixed': True}"
                 />
             </xpath>
             <xpath
                 expr="//field[@name='invoice_line_ids']/form/sheet/group/field[@name='discount']"
                 position="before"
             >
-                <field name="discount_fixed" groups="base.group_no_one" />
-            </xpath>
-            <xpath
-                expr="//field[@name='line_ids']/tree/field[@name='discount']"
-                position="before"
-            >
-                <field name="discount_fixed" invisible="1" />
+                <field
+                    name="discount_fixed"
+                    groups="account_invoice_fixed_discount.group_fixed_discount"
+                    context="{'ignore_discount_fixed': True}"
+                />
             </xpath>
         </field>
     </record>