diff --git a/addons/sale_project/models/project.py b/addons/sale_project/models/project.py
index 10bb47f2a5d..204ed64dd5f 100644
--- a/addons/sale_project/models/project.py
+++ b/addons/sale_project/models/project.py
@@ -12,7 +12,7 @@ class Project(models.Model):
 
     sale_line_id = fields.Many2one(
         'sale.order.line', 'Sales Order Item', copy=False,
-        compute="_compute_sale_line_id", store=True, readonly=False,
+        compute="_compute_sale_line_id", store=True, readonly=False, index=True,
         domain="[('is_service', '=', True), ('is_expense', '=', False), ('state', 'in', ['sale', 'done']), ('order_partner_id', '=?', partner_id), '|', ('company_id', '=', False), ('company_id', '=', company_id)]",
         help="Sales order item to which the project is linked. Link the timesheet entry to the sales order item defined on the project. "
         "Only applies on tasks without sale order item defined, and if the employee is not in the 'Employee/Sales Order Item Mapping' of the project.")
@@ -61,7 +61,7 @@ class ProjectTask(models.Model):
     sale_order_id = fields.Many2one('sale.order', 'Sales Order', compute='_compute_sale_order_id', store=True, help="Sales order to which the task is linked.")
     sale_line_id = fields.Many2one(
         'sale.order.line', 'Sales Order Item', domain="[('company_id', '=', company_id), ('is_service', '=', True), ('order_partner_id', 'child_of', commercial_partner_id), ('is_expense', '=', False), ('state', 'in', ['sale', 'done'])]",
-        compute='_compute_sale_line', recursive=True, store=True, readonly=False, copy=False, tracking=True,
+        compute='_compute_sale_line', recursive=True, store=True, readonly=False, copy=False, tracking=True, index=True,
         help="Sales Order Item to which the time spent on this task will be added, in order to be invoiced to your customer.")
     project_sale_order_id = fields.Many2one('sale.order', string="Project's sale order", related='project_id.sale_order_id')
     invoice_count = fields.Integer("Number of invoices", related='sale_order_id.invoice_count')
diff --git a/addons/sale_project/models/sale_order.py b/addons/sale_project/models/sale_order.py
index b91be8db811..10795b84a15 100644
--- a/addons/sale_project/models/sale_order.py
+++ b/addons/sale_project/models/sale_order.py
@@ -353,3 +353,24 @@ class SaleOrderLine(models.Model):
                         project = map_so_project[so_line.order_id.id]
                 if not so_line.task_id:
                     so_line._timesheet_create_task(project=project)
+
+    def _prepare_invoice_line(self, **optional_values):
+        """
+            If the sale order line isn't linked to a sale order which already have a default analytic account,
+            this method allows to retrieve the analytic account which is linked to project or task directly linked
+            to this sale order line, or the analytic account of the project which uses this sale order line, if it exists.
+        """
+        values = super(SaleOrderLine, self)._prepare_invoice_line(**optional_values)
+        if not values['analytic_account_id']:
+            if self.project_id.analytic_account_id:
+                values['analytic_account_id'] = self.project_id.analytic_account_id
+            elif self.task_id.project_id.analytic_account_id:
+                values['analytic_account_id'] = self.task_id.project_id.analytic_account_id
+            elif self.is_service and not self.is_expense:
+                project_analytic_account_id = self.env['project.project'].read_group([
+                    '|', ('sale_line_id', '=', self.id), ('task_ids.sale_line_id', '=', self.id)
+                ], ['analytic_account_id'], ['analytic_account_id'])
+                analytic_account_ids = {rec['analytic_account_id'][0] for rec in project_analytic_account_id}
+                if len(analytic_account_ids) == 1:
+                    values['analytic_account_id'] = analytic_account_ids.pop()
+        return values