diff --git a/sale_timesheet_existing_project/__manifest__.py b/sale_timesheet_existing_project/__manifest__.py
index 59d62a7ebb..3ae525a873 100644
--- a/sale_timesheet_existing_project/__manifest__.py
+++ b/sale_timesheet_existing_project/__manifest__.py
@@ -1,4 +1,5 @@
 # Copyright 2019 Tecnativa - Pedro M. Baeza
+# Copyright 2020 Sergio Corato <https://github.com/sergiocorato>
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
 
 {
@@ -12,7 +13,9 @@
         "views/product_template_views.xml",
         "views/sale_order_views.xml",
     ],
-    "author": "Tecnativa, Odoo Community Association (OCA)",
+    "author": "Tecnativa, "
+              "Sergio Corato, "
+              "Odoo Community Association (OCA)",
     "website": "https://github.com/OCA/timesheet",
     "license": "AGPL-3",
     "installable": True,
diff --git a/sale_timesheet_existing_project/models/sale_order.py b/sale_timesheet_existing_project/models/sale_order.py
index 61f692f769..33c0ada137 100644
--- a/sale_timesheet_existing_project/models/sale_order.py
+++ b/sale_timesheet_existing_project/models/sale_order.py
@@ -1,7 +1,9 @@
 # Copyright 2019 Tecnativa - Pedro M. Baeza
+# Copyright 2020 Sergio Corato <https://github.com/sergiocorato>
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
 
-from odoo import api, fields, models
+from odoo import api, fields, models, _
+from odoo.exceptions import UserError
 
 
 class SaleOrder(models.Model):
@@ -17,7 +19,8 @@ class SaleOrder(models.Model):
                " ('analytic_account_id', '!=', False),"
                " ('company_id', '=', company_id)]",
         readonly=True,
-        states={'draft': [('readonly', False)], 'sent': [('readonly', False)]},
+        states={'draft': [('readonly', False)], 'sent': [('readonly', False)],
+                'sale': [('readonly', False)], 'done': [('readonly', False)]},
         help='Select a non billable project on which tasks can be created.')
 
     @api.depends('order_line.product_id.service_tracking')
@@ -32,6 +35,17 @@ def _compute_visible_project(self):
                 in order.order_line.mapped('product_id.service_tracking')
             )
 
+    @api.multi
+    def write(self, vals):
+        res = super(SaleOrder, self).write(vals)
+        for order in self:
+            if order.state == 'sale' and order.visible_project and not \
+                    order.project_id and any(order.mapped('order_line.project_id')):
+                raise UserError(_('Missing project in sale order, but almost one '
+                                  'line of the order have a project: assign one of '
+                                  'these projects to the sale order!'))
+        return res
+
 
 class SaleOrderLine(models.Model):
     _inherit = "sale.order.line"
diff --git a/sale_timesheet_existing_project/readme/DESCRIPTION.rst b/sale_timesheet_existing_project/readme/DESCRIPTION.rst
index 42ce449b0a..92666d8b25 100644
--- a/sale_timesheet_existing_project/readme/DESCRIPTION.rst
+++ b/sale_timesheet_existing_project/readme/DESCRIPTION.rst
@@ -1,3 +1,7 @@
 This module restores the behavior present in previous version (and restored
 again in v13) of being able to reuse existing projects for generating the
 tasks when confirming a sales order with service tracking.
+
+When sale order is confirmed, product generating task can be added, but only
+the first without adding a project to the sale order, avoiding the creation
+of multiple projects.
diff --git a/sale_timesheet_existing_project/tests/test_sale_timesheet_existing_project.py b/sale_timesheet_existing_project/tests/test_sale_timesheet_existing_project.py
index 3fa1194504..f3b6a97385 100644
--- a/sale_timesheet_existing_project/tests/test_sale_timesheet_existing_project.py
+++ b/sale_timesheet_existing_project/tests/test_sale_timesheet_existing_project.py
@@ -2,6 +2,7 @@
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
 
 from odoo.tests import common
+from odoo.exceptions import UserError
 
 
 class TestSaleTimesheetExistingProject(common.SavepointCase):
@@ -25,6 +26,13 @@ def setUpClass(cls):
             'order_id': cls.order.id,
             'product_id': cls.product.id,
         })
+        cls.order1 = cls.env['sale.order'].create({
+            'partner_id': cls.partner.id,
+        })
+        cls.line1 = cls.env['sale.order.line'].create({
+            'order_id': cls.order1.id,
+            'product_id': cls.env.ref('product.product_product_10').id,
+        })
 
     def test_onchange_product_service_tracking(self):
         self.product.project_id = self.project.id
@@ -63,3 +71,26 @@ def test_sale_timesheet_new_project(self):
         self.assertNotEqual(self.line.task_id.project_id, self.project)
         self.assertIn(self.order.name, self.line.project_id.name)
         self.assertEqual(line2.project_id, self.line.project_id)
+
+    def test_sale_timesheet_new_project_set_in_sale_state(self):
+        self.product.project_template_id = False
+        self.order1.write({
+            'order_line': [(
+                0, 0, {'product_id': self.product.id}
+            )]
+        })
+        self.order1.action_confirm()
+        self.assertEqual(self.order1.state, 'sale')
+        self.assertEqual(len(self.order1.mapped('order_line.project_id')), 1)
+        with self.assertRaises(UserError):
+            self.order1.write({
+                'order_line': [(
+                    0, 0, {'product_id': self.product.id}
+                )]
+            })
+        self.order1.project_id = self.project.id
+        self.order1.write({
+            'order_line': [(
+                0, 0, {'product_id': self.product.id}
+            )]
+        })