diff --git a/addons/sale_timesheet/models/project.py b/addons/sale_timesheet/models/project.py
index 2e79e71ab76..9af4cd514b6 100644
--- a/addons/sale_timesheet/models/project.py
+++ b/addons/sale_timesheet/models/project.py
@@ -340,8 +340,10 @@ class ProjectTask(models.Model):
     def _get_default_partner_id(self, project, parent):
         res = super()._get_default_partner_id(project, parent)
         if not res and project:
-            if project.pricing_type == 'employee_rate':
-                return project.sale_line_employee_ids.sale_line_id.order_partner_id[:1]
+            # project in sudo if the current user is a portal user.
+            related_project = project if not self.user_has_groups('!base.group_user,base.group_portal') else project.sudo()
+            if related_project.pricing_type == 'employee_rate':
+                return related_project.sale_line_employee_ids.sale_line_id.order_partner_id[:1]
         return res
 
     sale_order_id = fields.Many2one(domain="['|', '|', ('partner_id', '=', partner_id), ('partner_id', 'child_of', commercial_partner_id), ('partner_id', 'parent_of', partner_id)]")