diff --git a/addons/project/models/project.py b/addons/project/models/project.py
index a36e7209dd4..cf5ef270375 100644
--- a/addons/project/models/project.py
+++ b/addons/project/models/project.py
@@ -415,7 +415,7 @@ class Task(models.Model):
     @api.constrains('date_start', 'date_end')
     def _check_dates(self):
         if any(self.filtered(lambda task: task.date_start and task.date_end and task.date_start > task.date_end)):
-            return ValidationError(_('Error ! Task starting date must be lower than its ending date.'))
+            raise ValidationError(_('Error ! Task starting date must be lower than its ending date.'))
 
     # Override view according to the company definition
     @api.model