diff --git a/bbs/board.py b/bbs/board.py
index 6c622c67c..252771682 100644
--- a/bbs/board.py
+++ b/bbs/board.py
@@ -298,7 +298,7 @@ async def create_post(
     form_data: Annotated[WriteForm, Depends()],
     service: Annotated[CreatePostService, Depends(CreatePostService.async_init)],
     file_service: Annotated[BoardFileService, Depends()],
-    parent_id: int = Form(None),
+    parent_id: int = Form(0),
     notice: bool = Form(False),
     secret: str = Form(""),
     html: str = Form(""),
diff --git a/core/formclass.py b/core/formclass.py
index 185d7c9b4..e363c811b 100644
--- a/core/formclass.py
+++ b/core/formclass.py
@@ -456,7 +456,7 @@ class WriteCommentForm:
     wr_name: str = Form(None)
     wr_password: str = Form(None)
     wr_secret: str = Form(None)
-    comment_id: int = Form(None)
+    comment_id: int = Form(0)
 
 
 @dataclass