Index: include/__tuple
===================================================================
--- include/__tuple
+++ include/__tuple
@@ -22,7 +22,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _Tp> class _LIBCPP_TEMPLATE_VIS tuple_size;
+template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size;
 
 #if !defined(_LIBCPP_CXX03_LANG)
 template <class _Tp, class...>
@@ -29,7 +29,7 @@
 using __enable_if_tuple_size_imp = _Tp;
 
 template <class _Tp>
-class _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
+struct _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
     const _Tp,
     typename enable_if<!is_volatile<_Tp>::value>::type,
     integral_constant<size_t, sizeof(tuple_size<_Tp>)>>>
@@ -36,7 +36,7 @@
     : public integral_constant<size_t, tuple_size<_Tp>::value> {};
 
 template <class _Tp>
-class _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
+struct _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
     volatile _Tp,
     typename enable_if<!is_const<_Tp>::value>::type,
     integral_constant<size_t, sizeof(tuple_size<_Tp>)>>>
@@ -43,15 +43,15 @@
     : public integral_constant<size_t, tuple_size<_Tp>::value> {};
 
 template <class _Tp>
-class _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
+struct _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
     const volatile _Tp,
     integral_constant<size_t, sizeof(tuple_size<_Tp>)>>>
     : public integral_constant<size_t, tuple_size<_Tp>::value> {};
 
 #else
-template <class _Tp> class _LIBCPP_TEMPLATE_VIS tuple_size<const _Tp> : public tuple_size<_Tp> {};
-template <class _Tp> class _LIBCPP_TEMPLATE_VIS tuple_size<volatile _Tp> : public tuple_size<_Tp> {};
-template <class _Tp> class _LIBCPP_TEMPLATE_VIS tuple_size<const volatile _Tp> : public tuple_size<_Tp> {};
+template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size<const _Tp> : public tuple_size<_Tp> {};
+template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size<volatile _Tp> : public tuple_size<_Tp> {};
+template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size<const volatile _Tp> : public tuple_size<_Tp> {};
 #endif
 
 template <size_t _Ip, class _Tp> class _LIBCPP_TEMPLATE_VIS tuple_element;
@@ -165,7 +165,7 @@
 template <class... _Tp> struct __tuple_like<tuple<_Tp...> > : true_type {};
 
 template <class ..._Tp>
-class _LIBCPP_TEMPLATE_VIS tuple_size<tuple<_Tp...> >
+struct _LIBCPP_TEMPLATE_VIS tuple_size<tuple<_Tp...> >
     : public integral_constant<size_t, sizeof...(_Tp)>
 {
 };
@@ -291,7 +291,7 @@
 
 
 template <class ..._Tp>
-class _LIBCPP_TEMPLATE_VIS tuple_size<__tuple_types<_Tp...> >
+struct _LIBCPP_TEMPLATE_VIS tuple_size<__tuple_types<_Tp...> >
     : public integral_constant<size_t, sizeof...(_Tp)>
 {
 };
Index: include/array
===================================================================
--- include/array
+++ include/array
@@ -91,7 +91,7 @@
 template <class T, size_t N >
   void swap(array<T,N>& x, array<T,N>& y) noexcept(noexcept(x.swap(y))); // C++17
 
-template <class T> class tuple_size;
+template <class T> struct tuple_size;
 template <size_t I, class T> class tuple_element;
 template <class T, size_t N> struct tuple_size<array<T, N>>;
 template <size_t I, class T, size_t N> struct tuple_element<I, array<T, N>>;
@@ -430,7 +430,7 @@
 }
 
 template <class _Tp, size_t _Size>
-class _LIBCPP_TEMPLATE_VIS tuple_size<array<_Tp, _Size> >
+struct _LIBCPP_TEMPLATE_VIS tuple_size<array<_Tp, _Size> >
     : public integral_constant<size_t, _Size> {};
 
 template <size_t _Ip, class _Tp, size_t _Size>
Index: include/tuple
===================================================================
--- include/tuple
+++ include/tuple
@@ -84,8 +84,8 @@
   constexpr T make_from_tuple(Tuple&& t); // C++17
 
 // 20.4.1.4, tuple helper classes:
-template <class T> class tuple_size; // undefined
-template <class... T> class tuple_size<tuple<T...>>;
+template <class T> struct tuple_size; // undefined
+template <class... T> struct tuple_size<tuple<T...>>;
 template <class T>
  inline constexpr size_t tuple_size_v = tuple_size<T>::value; // C++17
 template <size_t I, class T> class tuple_element; // undefined
Index: include/utility
===================================================================
--- include/utility
+++ include/utility
@@ -103,7 +103,7 @@
 struct piecewise_construct_t { };
 inline constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
 
-template <class T> class tuple_size;
+template <class T> struct tuple_size;
 template <size_t I, class T> class tuple_element;
 
 template <class T1, class T2> struct tuple_size<pair<T1, T2> >;
@@ -663,7 +663,7 @@
 #endif  // _LIBCPP_CXX03_LANG
 
 template <class _T1, class _T2>
-  class _LIBCPP_TEMPLATE_VIS tuple_size<pair<_T1, _T2> >
+  struct _LIBCPP_TEMPLATE_VIS tuple_size<pair<_T1, _T2> >
     : public integral_constant<size_t, 2> {};
 
 template <size_t _Ip, class _T1, class _T2>
Index: test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_incomplete.fail.cpp
===================================================================
--- test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_incomplete.fail.cpp
+++ test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_incomplete.fail.cpp
@@ -12,7 +12,7 @@
 // template <class... Types> class tuple;
 
 // template <class... Types>
-//   class tuple_size<tuple<Types...>>
+//   struct tuple_size<tuple<Types...>>
 //     : public integral_constant<size_t, sizeof...(Types)> { };
 
 // UNSUPPORTED: c++98, c++03
@@ -26,19 +26,19 @@
 struct Dummy3 {};
 
 template <>
-class std::tuple_size<Dummy1> {
+struct std::tuple_size<Dummy1> {
 public:
   static size_t value;
 };
 
 template <>
-class std::tuple_size<Dummy2> {
+struct std::tuple_size<Dummy2> {
 public:
   static void value() {}
 };
 
 template <>
-class std::tuple_size<Dummy3> {};
+struct std::tuple_size<Dummy3> {};
 
 int main()
 {
Index: test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_incomplete.pass.cpp
===================================================================
--- test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_incomplete.pass.cpp
+++ test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_incomplete.pass.cpp
@@ -12,7 +12,7 @@
 // template <class... Types> class tuple;
 
 // template <class... Types>
-//   class tuple_size<tuple<Types...>>
+//   struct tuple_size<tuple<Types...>>
 //     : public integral_constant<size_t, sizeof...(Types)> { };
 
 // XFAIL: gcc-4.9
@@ -31,7 +31,7 @@
 struct Dummy2 {};
 
 namespace std {
-template <> class tuple_size<Dummy1> : public integral_constant<size_t, 0> {};
+template <> struct tuple_size<Dummy1> : public integral_constant<size_t, 0> {};
 }
 
 template <class T>
Index: test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_structured_bindings.pass.cpp
===================================================================
--- test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_structured_bindings.pass.cpp
+++ test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_structured_bindings.pass.cpp
@@ -12,7 +12,7 @@
 // template <class... Types> class tuple;
 
 // template <class... Types>
-//   class tuple_size<tuple<Types...>>
+//   struct tuple_size<tuple<Types...>>
 //     : public integral_constant<size_t, sizeof...(Types)> { };
 
 // UNSUPPORTED: c++98, c++03, c++11, c++14
@@ -129,7 +129,7 @@
 }
 
 template <>
-class std::tuple_size<Test> {
+struct std::tuple_size<Test> {
 public:
   static const size_t value = 1;
 };