diff --git a/libcxx/include/__type_traits/conditional.h b/libcxx/include/__type_traits/conditional.h
--- a/libcxx/include/__type_traits/conditional.h
+++ b/libcxx/include/__type_traits/conditional.h
@@ -26,6 +26,9 @@
 template <bool _Bp, class _If, class _Then> using conditional_t = typename conditional<_Bp, _If, _Then>::type;
 #endif
 
+// Helper so we can use "conditional_t" in all language versions.
+template <bool _Bp, class _If, class _Then> using __conditional_t = typename conditional<_Bp, _If, _Then>::type;
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___TYPE_TRAITS_CONDITIONAL_H
diff --git a/libcxx/include/charconv b/libcxx/include/charconv
--- a/libcxx/include/charconv
+++ b/libcxx/include/charconv
@@ -487,16 +487,21 @@
 inline _LIBCPP_HIDE_FROM_ABI to_chars_result
 to_chars(char* __first, char* __last, _Tp __value)
 {
-    return __to_chars_itoa(__first, __last, __value, is_signed<_Tp>());
+  using _Type = __make_32_64_or_128_bit_t<_Tp>;
+  static_assert(!is_same<_Type, void>::value, "unsupported integral type used in to_chars");
+  static_assert(sizeof(_Tp) <= sizeof(int64_t), "128-bit integral support isn't available yet in to_chars");
+  return std::__to_chars_itoa(__first, __last, static_cast<_Type>(__value), is_signed<_Tp>());
 }
 
 template <typename _Tp, typename enable_if<is_integral<_Tp>::value, int>::type = 0>
 inline _LIBCPP_HIDE_FROM_ABI to_chars_result
 to_chars(char* __first, char* __last, _Tp __value, int __base)
 {
-    _LIBCPP_ASSERT(2 <= __base && __base <= 36, "base not in [2, 36]");
-    return __to_chars_integral(__first, __last, __value, __base,
-                               is_signed<_Tp>());
+  _LIBCPP_ASSERT(2 <= __base && __base <= 36, "base not in [2, 36]");
+
+  using _Type = __make_32_64_or_128_bit_t<_Tp>;
+  static_assert(sizeof(_Tp) <= sizeof(int64_t), "128-bit integral support isn't available yet in to_chars");
+  return std::__to_chars_integral(__first, __last, static_cast<_Type>(__value), __base, is_signed<_Tp>());
 }
 
 template <typename _It, typename _Tp, typename _Fn, typename... _Ts>
diff --git a/libcxx/include/type_traits b/libcxx/include/type_traits
--- a/libcxx/include/type_traits
+++ b/libcxx/include/type_traits
@@ -517,6 +517,7 @@
 #include <__type_traits/void_t.h>
 #include <__utility/declval.h>
 #include <cstddef>
+#include <cstdint>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -1020,6 +1021,23 @@
 }
 #endif
 
+template <class _Tp, class _Up>
+using __copy_unsigned_t = __conditional_t<is_unsigned<_Tp>::value, typename make_unsigned<_Up>::type, _Up>;
+
+template <class _Tp>
+using __make_32_64_or_128_bit_t =
+  __copy_unsigned_t<_Tp,
+    __conditional_t<sizeof(_Tp) <= sizeof(int32_t),    int32_t,
+    __conditional_t<sizeof(_Tp) <= sizeof(int64_t),    int64_t,
+#ifndef _LIBCPP_HAS_NO_INT128
+    __conditional_t<sizeof(_Tp) <= sizeof(__int128_t), __int128_t,
+    /* else */                                         void>
+#else
+    /* else */                                         void
+#endif
+	>>
+  >;
+
 #if _LIBCPP_STD_VER > 17
 // Let COND_RES(X, Y) be:
 template <class _Tp, class _Up>