diff --git a/mie/dialect/func/op/func.c b/mie/dialect/func/op/func.c
index 22b0b39..e591604 100644
--- a/mie/dialect/func/op/func.c
+++ b/mie/dialect/func/op/func.c
@@ -130,6 +130,7 @@ struct mie_op *mie_func_put_func(
 MIE_OP_DEFINITION_BEGIN(mie_func_func, "func")
 	MIE_OP_DEFINITION_PRINT(print);
 	MIE_OP_DEFINITION_PARSE(parse);
+	MIE_OP_DEFINITION_TRAIT("builtin", "isolated-from-above");
 	MIE_OP_INTERFACE_BEGIN("builtin", "symbol", struct mie_symbol)
 		MIE_OP_INTERFACE_FUNC(sym_get_name) = NULL;
 	MIE_OP_INTERFACE_END()