diff --git a/addons/website_forum/models/forum.py b/addons/website_forum/models/forum.py
index b071a43f4d6..c707dccf3ee 100644
--- a/addons/website_forum/models/forum.py
+++ b/addons/website_forum/models/forum.py
@@ -337,7 +337,7 @@ class Post(models.Model):
     is_correct = fields.Boolean('Correct', help='Correct answer or answer accepted')
     parent_id = fields.Many2one('forum.post', string='Question', ondelete='cascade', readonly=True, index=True)
     self_reply = fields.Boolean('Reply to own question', compute='_is_self_reply', store=True)
-    child_ids = fields.One2many('forum.post', 'parent_id', string='Post Answers', domain=lambda self: [('forum_id', '=', self.forum_id.id)])
+    child_ids = fields.One2many('forum.post', 'parent_id', string='Post Answers', domain=lambda self: [('forum_id', 'in', self.forum_id.ids)])
     child_count = fields.Integer('Answers', compute='_get_child_count', store=True)
     uid_has_answered = fields.Boolean('Has Answered', compute='_get_uid_has_answered')
     has_validated_answer = fields.Boolean('Is answered', compute='_get_has_validated_answer', store=True)