Index: libcxx/include/__config
===================================================================
--- libcxx/include/__config
+++ libcxx/include/__config
@@ -38,7 +38,7 @@
 #  define _LIBCPP_ABI_VERSION 1
 #endif
 
-#ifndef __STDC_HOSTED__
+#if __STDC_HOSTED__ == 0
 #  define _LIBCPP_FREESTANDING
 #endif
 
Index: libcxx/test/libcxx/libcpp_freestanding.sh.cpp
===================================================================
--- /dev/null
+++ libcxx/test/libcxx/libcpp_freestanding.sh.cpp
@@ -0,0 +1,21 @@
+// -*- 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} -fsyntax-only %s
+// RUN: %{cxx} %{flags} %{compile_flags} -fsyntax-only -ffreestanding -DFREESTANDING %s
+
+#include <__config>
+
+#if defined(FREESTANDING) != defined(_LIBCPP_FREESTANDING)
+#error _LIBCPP_FREESTANDING should be defined in freestanding mode and not \
+       defined in non-freestanding mode
+#endif