diff --git a/runtime/lambda/closure_builder.h b/runtime/lambda/closure_builder.h
index 542e12a..23eb484 100644
--- a/runtime/lambda/closure_builder.h
+++ b/runtime/lambda/closure_builder.h
@@ -40,13 +40,12 @@
 //
 // The mutator lock must be held for the duration of the lifetime of this object,
 // since it needs to temporarily store heap references into an internal list.
-class ClosureBuilder : ValueObject {
+class ClosureBuilder {
  public:
   using ShortyTypeEnum = decltype(ShortyFieldType::kByte);
 
-
   // Mark this primitive value to be captured as the specified type.
-  template <typename T, ShortyTypeEnum kShortyType>
+  template <typename T, ShortyTypeEnum kShortyType = ShortyFieldTypeSelectEnum<T>::value>
   void CaptureVariablePrimitive(T value);
 
   // Mark this object reference to be captured.
@@ -63,6 +62,9 @@
   // Returns how many variables have been captured so far.
   size_t GetCaptureCount() const;
 
+  // Get the list of captured variables' shorty field types.
+  const std::string& GetCapturedVariableShortyTypes() const;
+
   // Creates a closure in-place and writes out the data into 'memory'.
   // Memory must be at least 'GetSize' bytes large.
   // All previously marked data to be captured is now written out.
@@ -93,6 +95,7 @@
   size_t size_ = kInitialSize;
   bool is_dynamic_size_ = false;
   std::vector<ShortyFieldTypeTraits::MaxType> values_;
+  std::string shorty_types_;
 };
 
 }  // namespace lambda