diff --git a/include/llvm/ADT/Optional.h b/include/llvm/ADT/Optional.h
index ae8344da76a..cb45c78e2c1 100644
--- a/include/llvm/ADT/Optional.h
+++ b/include/llvm/ADT/Optional.h
@@ -29,6 +29,8 @@ class Optional {
   AlignedCharArrayUnion<T> storage;
   bool hasVal;
 public:
+  typedef T value_type;
+
   Optional(NoneType) : hasVal(false) {}
   explicit Optional() : hasVal(false) {}
   Optional(const T &y) : hasVal(true) {