diff --git a/aidl_language.h b/aidl_language.h
index 6638e0e..1df620e 100644
--- a/aidl_language.h
+++ b/aidl_language.h
@@ -601,6 +601,8 @@
   std::unique_ptr<AidlTypeSpecifier> ref_type_;
   std::string field_name_;
   const std::string comments_;
+  mutable bool is_evaluating_ = false;  // to prevent re-entrant CheckValid with circular references
+  mutable bool is_validating_ = false;  // to prevent re-entrant CheckValid with circular references
 };
 
 class AidlUnaryConstExpression : public AidlConstantValue {