diff --git a/libcxx/include/__format/format_arg.h b/libcxx/include/__format/format_arg.h
--- a/libcxx/include/__format/format_arg.h
+++ b/libcxx/include/__format/format_arg.h
@@ -37,21 +37,20 @@
 #if !defined(_LIBCPP_HAS_NO_CONCEPTS)
 
 namespace __format {
-/** The type stored in @ref basic_format_arg. */
+/// The type stored in @ref basic_format_arg.
+///
+/// @note The 128-bit types are unconditionally in the list to avoid the values
+/// of the enums to depend on the availability of 128-bit integers.
 enum class _LIBCPP_ENUM_VIS __arg_t : uint8_t {
   __none,
   __boolean,
   __char_type,
   __int,
   __long_long,
-#ifndef _LIBCPP_HAS_NO_INT128
   __i128,
-#endif
   __unsigned,
   __unsigned_long_long,
-#ifndef _LIBCPP_HAS_NO_INT128
   __u128,
-#endif
   __float,
   __double,
   __long_double,