diff --git a/addons/project/models/project.py b/addons/project/models/project.py
index 440b5b64dc2..888fa6c8b5c 100644
--- a/addons/project/models/project.py
+++ b/addons/project/models/project.py
@@ -936,7 +936,7 @@ class Task(models.Model):
     @api.depends('child_ids')
     def _compute_subtask_count(self):
         for task in self:
-            task.subtask_count = len(self._get_all_subtasks())
+            task.subtask_count = len(task._get_all_subtasks())
 
     @api.onchange('company_id')
     def _onchange_task_company(self):