diff --git a/include/llvm/ADT/STLExtras.h b/include/llvm/ADT/STLExtras.h
index 28f75949373..06a1756e26f 100644
--- a/include/llvm/ADT/STLExtras.h
+++ b/include/llvm/ADT/STLExtras.h
@@ -117,7 +117,9 @@ public:
           iterator_category;
   typedef typename std::iterator_traits<RootIt>::difference_type
           difference_type;
-  typedef typename UnaryFunc::result_type value_type;
+  typedef typename std::result_of<
+            UnaryFunc(decltype(*std::declval<RootIt>()))>
+          ::type value_type;
 
   typedef void pointer;
   //typedef typename UnaryFunc::result_type *pointer;