diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -1622,6 +1622,7 @@
           tok::kw___is_signed,
           tok::kw___is_standard_layout,
           tok::kw___is_trivial,
+          tok::kw___is_trivially_equality_comparable,
           tok::kw___is_trivially_assignable,
           tok::kw___is_trivially_constructible,
           tok::kw___is_trivially_copyable,
diff --git a/clang/test/SemaCXX/libcxx_is_trivially_equality_comparable_hack.cpp b/clang/test/SemaCXX/libcxx_is_trivially_equality_comparable_hack.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/libcxx_is_trivially_equality_comparable_hack.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -fsyntax-only -verify -std=gnu++20 -fms-extensions -Wno-microsoft %s
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -fsyntax-only -verify -std=gnu++2b -fms-extensions -Wno-microsoft %s
+
+template <class T, class U>
+struct Same {
+  static constexpr auto value = __is_same(T, U);
+};
+
+template <class T>
+struct __is_trivially_equality_comparable { // expected-warning{{keyword '__is_trivially_equality_comparable' will be made available as an identifier for the remainder of the translation unit}}
+  using type = T;
+};
+
+using A = Same<__is_trivially_equality_comparable<int>::type, __is_trivially_equality_comparable<int>::type>;