diff --git a/backend/oasst_backend/prompt_repository.py b/backend/oasst_backend/prompt_repository.py
index 95e7867e..c3728dfc 100644
--- a/backend/oasst_backend/prompt_repository.py
+++ b/backend/oasst_backend/prompt_repository.py
@@ -397,7 +397,7 @@ class PromptRepository:
             distinct_threads = distinct_threads.filter(Post.role == require_role)
         distinct_threads = distinct_threads.subquery()
 
-        random_thread = self.db.query(distinct_threads).order_by(func.random()).limit(1).subquery()
+        random_thread = self.db.query(distinct_threads).order_by(func.random()).limit(1)
         thread_posts = self.db.query(Post).filter(Post.thread_id.in_(random_thread)).all()
         return thread_posts
 
@@ -443,7 +443,7 @@ class PromptRepository:
         if post_role:
             parent = parent.filter(Post.role == post_role)
 
-        parent = parent.order_by(func.random()).limit(1).subquery()
+        parent = parent.order_by(func.random()).limit(1)
         replies = self.db.query(Post).filter(Post.parent_id.in_(parent)).order_by(func.random()).limit(max_size).all()
         if not replies:
             raise OasstError("No replies found", OasstErrorCode.NO_REPLIES_FOUND)