diff --git a/src/ast.rs b/src/ast.rs
index c64d698..907d0d6 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -911,6 +911,7 @@ where
 macro_rules! reference_newtype {
     ( $newtype_name:ident , $oldtype:ty ) => {
         #[derive(Debug)]
+        #[repr(transparent)]
         struct $newtype_name($oldtype);
 
         impl $newtype_name {