Index: clang/include/clang/Basic/TokenKinds.def
===================================================================
--- clang/include/clang/Basic/TokenKinds.def
+++ clang/include/clang/Basic/TokenKinds.def
@@ -435,6 +435,7 @@
 TYPE_TRAIT_2(__builtin_types_compatible_p, TypeCompatible, KEYNOCXX)
 KEYWORD(__builtin_va_arg            , KEYALL)
 KEYWORD(__extension__               , KEYALL)
+ALIAS("__ieee128", __float128       , KEYALL)
 KEYWORD(__float128                  , KEYALL)
 KEYWORD(__imag                      , KEYALL)
 KEYWORD(__int128                    , KEYALL)
Index: clang/test/Sema/128bitfloat.cpp
===================================================================
--- clang/test/Sema/128bitfloat.cpp
+++ clang/test/Sema/128bitfloat.cpp
@@ -6,6 +6,11 @@
 // RUN: %clang_cc1 -triple x86_64-windows-msvc -verify -std=c++11 %s
 
 #if defined(__FLOAT128__) || defined(__SIZEOF_FLOAT128__)
+
+template <typename> struct __is_float128 { static constexpr bool value = false; };
+template <> struct __is_float128<__float128> { static constexpr bool value = true; };
+static_assert(__is_float128<__ieee128>::value, "__ieee128 aliases to __float128");
+
 __float128 f;
 template<typename> struct __is_floating_point_helper {};
 template<> struct __is_floating_point_helper<__float128> {};