diff --git a/aidl_language.h b/aidl_language.h
index db92535..c2cffd6 100644
--- a/aidl_language.h
+++ b/aidl_language.h
@@ -22,6 +22,7 @@
 #include <unordered_set>
 #include <vector>
 
+#include <android-base/result.h>
 #include <android-base/strings.h>
 
 #include "aidl_typenames.h"
@@ -38,6 +39,7 @@
 using android::aidl::CodeWriter;
 using android::aidl::Comments;
 using android::aidl::Options;
+using android::base::Result;
 using std::shared_ptr;
 using std::string;
 using std::unique_ptr;
@@ -281,6 +283,8 @@
   void TraverseChildren(std::function<void(const AidlNode&)> traverse) const override;
   void DispatchVisit(AidlVisitor& v) const override { v.Visit(*this); }
 
+  Result<unique_ptr<perm::Expression>> EnforceExpression() const;
+
  private:
   struct ParamType {
     std::string name;