diff --git a/sub_project/models/sub_project.py b/sub_project/models/sub_project.py
index d83c945..3a0048a 100755
--- a/sub_project/models/sub_project.py
+++ b/sub_project/models/sub_project.py
@@ -7,7 +7,7 @@ class SubProject(models.Model):
 
     is_sub_project = fields.Boolean("Is Sub Project")
     sub_project = fields.Many2many('project.project', 'project_subproject_rel', 'project_id', 'id',
-                                   domain="[('is_sub_project', '=', True)]", string='Sub Project')
+                                   domain="[('is_sub_project', '=', True),('parent_project', '=', False)]", string='Sub Project')
     parent_project = fields.Many2one('project.project', domain="[('is_sub_project', '=', False)]", string='Parent Project')
 
     @api.onchange('parent_project', 'sub_project')
@@ -21,6 +21,7 @@ class SubProject(models.Model):
 
 
 
+
 class InheritProjectTask(models.Model):
     _inherit = 'project.task'