diff --git a/addons/sale_service/models/timesheet.py b/addons/sale_service/models/timesheet.py
index f4f235a8872..d9de3af5e9c 100644
--- a/addons/sale_service/models/timesheet.py
+++ b/addons/sale_service/models/timesheet.py
@@ -58,7 +58,7 @@ class account_analytic_line(models.Model):
     def _update_values(self, values):
         if values.get('task_id', False):
             task = self.env['project.task'].browse(values['task_id'])
-            values['so_line'] = task.sale_line_id and task.sale_line_id.id or False
+            values['so_line'] = task.sale_line_id and task.sale_line_id.id or values.get('so_line', False)
 
     @api.model
     def create(self, values):