diff --git a/include/bitset b/include/bitset
index e4c01e6..7ad332c 100644
--- a/include/bitset
+++ b/include/bitset
@@ -150,6 +150,10 @@ _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <size_t _N_words, size_t _Size>
@@ -289,9 +293,9 @@ inline
 _LIBCPP_CONSTEXPR
 __bitset<_N_words, _Size>::__bitset(unsigned long long __v) _NOEXCEPT
 #ifndef _LIBCPP_CXX03_LANG
-#if __SIZEOF_SIZE_T__ == 8
+#if SIZE_MAX == 0xffffffffffffffffULL
     : __first_{__v}
-#elif __SIZEOF_SIZE_T__ == 4
+#elif SIZE_MAX == 0xffffffffULL
     : __first_{static_cast<__storage_type>(__v),
                 _Size >= 2 * __bits_per_word ? static_cast<__storage_type>(__v >> __bits_per_word)
                 : static_cast<__storage_type>((__v >> __bits_per_word) & (__storage_type(1) << (_Size - __bits_per_word)) - 1)}