diff --git a/include/utility b/include/utility
index 535e3cb3a..f11d58019 100644
--- a/include/utility
+++ b/include/utility
@@ -52,7 +52,7 @@ template <class T>
     >::type
     move_if_noexcept(T& x) noexcept; // constexpr in C++14
 
-template <class T> constexpr add_const<T>_t& as_const(T& t) noexcept;      // C++17
+template <class T> constexpr add_const_t<T>& as_const(T& t) noexcept;      // C++17
 template <class T>                      void as_const(const T&&) = delete; // C++17
 
 template <class T> typename add_rvalue_reference<T>::type declval() noexcept;