diff --git a/addons/sale_timesheet/models/project_sale_line_employee_map.py b/addons/sale_timesheet/models/project_sale_line_employee_map.py
index 76a702d8b9f..d1b5e2322fa 100644
--- a/addons/sale_timesheet/models/project_sale_line_employee_map.py
+++ b/addons/sale_timesheet/models/project_sale_line_employee_map.py
@@ -10,7 +10,7 @@ class ProjectProductEmployeeMap(models.Model):
 
     project_id = fields.Many2one('project.project', "Project", required=True)
     employee_id = fields.Many2one('hr.employee', "Employee", required=True)
-    sale_line_id = fields.Many2one('sale.order.line', "Sale Order Item", domain=[('is_service', '=', True)])
+    sale_line_id = fields.Many2one('sale.order.line', "Sale Order Item", compute="_compute_sale_line_id", store=True, readonly=False, required=True, domain=[('is_service', '=', True)])
     company_id = fields.Many2one('res.company', string='Company', related='project_id.company_id')
     timesheet_product_id = fields.Many2one(
         'product.product', string='Service',
@@ -26,6 +26,10 @@ class ProjectProductEmployeeMap(models.Model):
         ('uniqueness_employee', 'UNIQUE(project_id,employee_id)', 'An employee cannot be selected more than once in the mapping. Please remove duplicate(s) and try again.'),
     ]
 
+    @api.depends('project_id.sale_order_id')
+    def _compute_sale_line_id(self):
+        self.filtered(lambda map_entry: not map_entry.project_id.sale_order_id and map_entry.sale_line_id).update({'sale_line_id': None})
+
     @api.depends('sale_line_id', 'sale_line_id.price_unit', 'timesheet_product_id')
     def _compute_price_unit(self):
         for line in self: