diff --git a/crates/fayalite/tests/hdl_types.rs b/crates/fayalite/tests/hdl_types.rs
index bed1a82..b8cbff3 100644
--- a/crates/fayalite/tests/hdl_types.rs
+++ b/crates/fayalite/tests/hdl_types.rs
@@ -32,6 +32,13 @@ pub struct S2<T = ()> {
     pub v: E<T>,
 }
 
+#[cfg(todo)]
+#[hdl(outline_generated)]
+pub struct S4<W: KnownSize, W2: KnownSize> {
+    pub v: UIntType<W>,
+    pub v2: SIntType<W2>,
+}
+
 // check that #[hdl] properly handles hygiene
 macro_rules! types_in_macros {
     ($a:ident, $b:ident, $c:ident, $d:ident, $e:ident, $f:ident, $A:ident, $B:ident, $C:ident, $D:ident, $E:ident, $F:ident) => {