diff --git a/lib/generator/ir.dart b/lib/generator/ir.dart
index 8157cc9..033cfc8 100644
--- a/lib/generator/ir.dart
+++ b/lib/generator/ir.dart
@@ -133,7 +133,7 @@ class Field {
 class TypeRef {
   final String base;
   
-  TypeRef(this.base);
+  const TypeRef(this.base);
   
   const TypeRef.integer() : this('integer');
   const TypeRef.string() : this('string');