diff --git a/addons/hr_timesheet/models/hr_timesheet.py b/addons/hr_timesheet/models/hr_timesheet.py
index 68a64a7fbde..c35b4365291 100644
--- a/addons/hr_timesheet/models/hr_timesheet.py
+++ b/addons/hr_timesheet/models/hr_timesheet.py
@@ -14,7 +14,7 @@ class AccountAnalyticLine(models.Model):
             result['employee_id'] = self.env['hr.employee'].search([('user_id', '=', result['user_id'])], limit=1).id
         return result
 
-    task_id = fields.Many2one('project.task', 'Task')
+    task_id = fields.Many2one('project.task', 'Task', index=True)
     project_id = fields.Many2one('project.project', 'Project', domain=[('allow_timesheets', '=', True)])
 
     employee_id = fields.Many2one('hr.employee', "Employee")
diff --git a/addons/project/models/project.py b/addons/project/models/project.py
index e391b533c2a..358348b92d7 100644
--- a/addons/project/models/project.py
+++ b/addons/project/models/project.py
@@ -455,7 +455,7 @@ class Task(models.Model):
     legend_blocked = fields.Char(related='stage_id.legend_blocked', string='Kanban Blocked Explanation', readonly=True, related_sudo=False)
     legend_done = fields.Char(related='stage_id.legend_done', string='Kanban Valid Explanation', readonly=True, related_sudo=False)
     legend_normal = fields.Char(related='stage_id.legend_normal', string='Kanban Ongoing Explanation', readonly=True, related_sudo=False)
-    parent_id = fields.Many2one('project.task', string='Parent Task')
+    parent_id = fields.Many2one('project.task', string='Parent Task', index=True)
     child_ids = fields.One2many('project.task', 'parent_id', string="Sub-tasks")
     subtask_project_id = fields.Many2one('project.project', related="project_id.subtask_project_id", string='Sub-task Project', readonly=True)
     subtask_count = fields.Integer(compute='_compute_subtask_count', type='integer', string="Sub-task count")
diff --git a/addons/sale_timesheet/models/sale_order.py b/addons/sale_timesheet/models/sale_order.py
index 8e662b21ee6..b0da56c02fa 100644
--- a/addons/sale_timesheet/models/sale_order.py
+++ b/addons/sale_timesheet/models/sale_order.py
@@ -136,7 +136,7 @@ class SaleOrder(models.Model):
 class SaleOrderLine(models.Model):
     _inherit = "sale.order.line"
 
-    task_id = fields.Many2one('project.task', 'Task', help="Task generated by the sales order item")
+    task_id = fields.Many2one('project.task', 'Task', index=True, help="Task generated by the sales order item")
     is_service = fields.Boolean("Is a Service", compute='_compute_is_service', store=True, help="Sales Order item should generate a task and/or a project, depending on the product settings.")
 
     @api.multi