Index: libcxx/include/__config
===================================================================
--- libcxx/include/__config
+++ libcxx/include/__config
@@ -38,10 +38,10 @@
 #  define _LIBCPP_ABI_VERSION 1
 #endif

-#ifndef __STDC_HOSTED__
+#if __STDC_HOSTED__ == 0
 #  define _LIBCPP_FREESTANDING
 #endif

 #ifndef _LIBCPP_STD_VER
 #  if  __cplusplus <= 201103L
 #    define _LIBCPP_STD_VER 11
Index: libcxx/test/libcxx/libcpp_freestanding.sh.cpp
===================================================================
--- /dev/null
+++ libcxx/test/libcxx/libcpp_freestanding.sh.cpp
@@ -0,0 +1,19 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// Test that _LIBCPP_FREESTANDING is not defined when -ffreestanding is not passed
+// to the compiler but defined when -ffreestanding is passed to the compiler.
+
+// RUN: %{cxx} %{flags} %{compile_flags} -E -dM %s | FileCheck %s
+// RUN: %{cxx} %{flags} %{compile_flags} -E -dM -ffreestanding %s | FileCheck -check-prefix=CHECK-FREESTANDING %s
+
+#include <__config>
+
+// CHECK-NOT: #define _LIBCPP_FREESTANDING
+// CHECK-FREESTANDING: #define _LIBCPP_FREESTANDING