diff --git a/python/mlc/dataclasses/utils.py b/python/mlc/dataclasses/utils.py
index 47156514..48d142f0 100644
--- a/python/mlc/dataclasses/utils.py
+++ b/python/mlc/dataclasses/utils.py
@@ -151,7 +151,7 @@ def _get_num_bytes(field_ty: Any) -> int:
             )
         )
     for field_name, field_ty_py in type_hints.items():
-        if field_name.startswith("_"):
+        if field_name.startswith("_mlc_"):
             continue
         field_ty = mlc_typing.from_py(field_ty_py)
         type_fields.append(