diff --git a/addons/account/models/partner.py b/addons/account/models/partner.py
index db91c34a07c..7a6e334b939 100644
--- a/addons/account/models/partner.py
+++ b/addons/account/models/partner.py
@@ -451,6 +451,7 @@ class ResPartner(models.Model):
         return {'domain': {'property_account_position_id': [('company_id', 'in', [company.id, False])]}}
 
     def can_edit_vat(self):
+        ''' Can't edit `vat` if there is (non draft) issued invoices. '''
         can_edit_vat = super(ResPartner, self).can_edit_vat()
         if not can_edit_vat:
             return can_edit_vat
diff --git a/addons/portal/models/res_partner.py b/addons/portal/models/res_partner.py
index 4c8d02943c5..064fa2ff04e 100644
--- a/addons/portal/models/res_partner.py
+++ b/addons/portal/models/res_partner.py
@@ -8,4 +8,7 @@ class ResPartner(models.Model):
     _inherit = 'res.partner'
 
     def can_edit_vat(self):
-        return True
+        ''' `vat` is a commercial field, synced between the parent (commercial
+        entity) and the children. Only the commercial entity should be able to
+        edit it (as in backend). '''
+        return not self.parent_id
diff --git a/addons/portal/views/portal_templates.xml b/addons/portal/views/portal_templates.xml
index 4059e2641fb..5783a1c24f8 100644
--- a/addons/portal/views/portal_templates.xml
+++ b/addons/portal/views/portal_templates.xml
@@ -378,8 +378,11 @@
                             <div class="clearfix" />
                             <div t-attf-class="form-group #{error.get('company_name') and 'o_has_error' or ''} col-xl-6">
                                 <label class="col-form-label label-optional" for="company_name">Company Name</label>
-                                <p t-if="partner.commercial_partner_id.is_company" t-attf-class="form-control #{error.get('company_name') and 'is-invalid' or ''}" t-esc="partner.commercial_company_name"/>
-                                <input t-else="" type="text" name="company_name" t-attf-class="form-control #{error.get('company_name') and 'is-invalid' or ''}" t-att-value="company_name or partner.company_name" t-att-readonly="None if partner.can_edit_vat() else '1'" t-att-title="None if partner.can_edit_vat() else 'Changing company name is not allowed once document(s) have been issued for your account. Please contact us directly for this operation.'"/>
+                                <!-- The <input> is replace by a <p> to avoid sending an unauthorized value on form submit.
+                                     The user might not have rights to change company_name but should still be able to see it.
+                                -->
+                                <p t-if="not partner.can_edit_vat()" t-attf-class="form-control" readonly="1" t-esc="partner.commercial_company_name" title="Changing company name is not allowed once document(s) have been issued for your account. Please contact us directly for this operation."/>
+                                <input t-else="" type="text" name="company_name" t-attf-class="form-control #{error.get('company_name') and 'is-invalid' or ''}" t-att-value="company_name or partner.commercial_company_name"/>
                             </div>
                             <div t-attf-class="form-group #{error.get('vat') and 'o_has_error' or ''} col-xl-6">
                                 <label class="col-form-label label-optional" for="vat">VAT Number</label>
diff --git a/addons/sale/models/res_partner.py b/addons/sale/models/res_partner.py
index a1f60defb2d..fac5165f55f 100644
--- a/addons/sale/models/res_partner.py
+++ b/addons/sale/models/res_partner.py
@@ -30,6 +30,7 @@ class ResPartner(models.Model):
                 partner = partner.parent_id
 
     def can_edit_vat(self):
+        ''' Can't edit `vat` if there is (non draft) issued SO. '''
         can_edit_vat = super(ResPartner, self).can_edit_vat()
         if not can_edit_vat:
             return can_edit_vat
diff --git a/addons/website_sale/views/templates.xml b/addons/website_sale/views/templates.xml
index 5b89ad4982b..47dd679ba31 100644
--- a/addons/website_sale/views/templates.xml
+++ b/addons/website_sale/views/templates.xml
@@ -1286,7 +1286,7 @@
             <t t-if="mode == ('new', 'billing') or (mode == ('edit', 'billing') and (can_edit_vat or 'vat' in checkout and checkout['vat']))">
                 <div t-attf-class="form-group #{error.get('company_name') and 'o_has_error' or ''} col-lg-6">
                     <label class="col-form-label font-weight-normal label-optional" for="company_name">Company Name</label>
-                    <input type="text" name="company_name" t-attf-class="form-control #{error.get('company_name') and 'is-invalid' or ''}" t-att-value="'company_name' in checkout and checkout['company_name']" t-att-readonly="'1' if 'vat' in checkout and checkout['vat'] and not can_edit_vat else None" t-att-title="'Changing company name is not allowed once document(s) have been issued for your account. Please contact us directly for this operation.' if 'vat' in checkout and checkout['vat'] and not can_edit_vat else None" />
+                    <input type="text" name="company_name" t-attf-class="form-control #{error.get('company_name') and 'is-invalid' or ''}" t-att-value="'commercial_company_name' in checkout and checkout['commercial_company_name'] or 'company_name' in checkout and checkout['company_name']" t-att-readonly="'1' if 'vat' in checkout and checkout['vat'] and not can_edit_vat else None" t-att-title="'Changing company name is not allowed once document(s) have been issued for your account. Please contact us directly for this operation.' if 'vat' in checkout and checkout['vat'] and not can_edit_vat else None" />
                 </div>
                 <div t-attf-class="form-group #{error.get('vat') and 'o_has_error' or ''} col-lg-6 div_vat">
                     <label class="col-form-label font-weight-normal label-optional" for="vat">TIN / VAT </label>