diff --git a/lang/src/son.rs b/lang/src/son.rs
index 351dab4..3ad3322 100644
--- a/lang/src/son.rs
+++ b/lang/src/son.rs
@@ -105,6 +105,9 @@ impl Nodes {
     }
 
     fn as_ty(&self, cint: Nid) -> ty::Id {
+        if self[citn].ty == ty::Id::NEVER {
+            return ty::Id::NEVER;
+        }
         debug_assert_eq!(self[cint].ty, ty::Id::TYPE);
         ty::Id::from(match self[cint].kind {
             Kind::CInt { value } => value as u64,