diff --git a/libcxx/include/__mbstate_t.h b/libcxx/include/__mbstate_t.h
--- a/libcxx/include/__mbstate_t.h
+++ b/libcxx/include/__mbstate_t.h
@@ -27,24 +27,24 @@
 // This does not define std::mbstate_t -- this only brings in the declaration
 // in the global namespace.
 
+#if __has_include(<bits/types/mbstate_t.h>)
+#  include <bits/types/mbstate_t.h> // works on most Unixes
+#elif __has_include(<sys/_types/_mbstate_t.h>)
+#  include <sys/_types/_mbstate_t.h> // works on Darwin
+#elif !defined(_LIBCPP_HAS_NO_WIDE_CHARACTERS) && __has_include_next(<wchar.h>)
+// Some older versions of <wchar.h> do not define this for clang, so we do it ourselves.
 // We define this here to support older versions of glibc <wchar.h> that do
 // not define this for clang. This is also set in libc++'s <wchar.h> header,
 // and we need to do so here too to avoid a different function signature given
 // a different include order.
-#ifdef __cplusplus
-#  define __CORRECT_ISO_CPP_WCHAR_H_PROTO
-#endif
-
-#if __has_include(<bits/types/mbstate_t.h>)
-#   include <bits/types/mbstate_t.h> // works on most Unixes
-#elif __has_include(<sys/_types/_mbstate_t.h>)
-#   include <sys/_types/_mbstate_t.h> // works on Darwin
-#elif !defined(_LIBCPP_HAS_NO_WIDE_CHARACTERS) && __has_include_next(<wchar.h>)
-#   include_next <wchar.h> // fall back to the C standard provider of mbstate_t
+#  ifdef __cplusplus
+#    define __CORRECT_ISO_CPP_WCHAR_H_PROTO
+#  endif
+#  include_next <wchar.h> // fall back to the C standard provider of mbstate_t
 #elif __has_include_next(<uchar.h>)
-#   include_next <uchar.h> // <uchar.h> is also required to make mbstate_t visible
+#  include_next <uchar.h> // <uchar.h> is also required to make mbstate_t visible
 #else
-#   error "We don't know how to get the definition of mbstate_t without <wchar.h> on your platform."
+#  error "We don't know how to get the definition of mbstate_t without <wchar.h> on your platform."
 #endif
 
 #endif // _LIBCPP___MBSTATE_T_H
diff --git a/libcxx/include/wchar.h b/libcxx/include/wchar.h
--- a/libcxx/include/wchar.h
+++ b/libcxx/include/wchar.h
@@ -116,13 +116,12 @@
 #  pragma GCC system_header
 #endif
 
+#  if __has_include_next(<wchar.h>)
 // We define this here to support older versions of glibc <wchar.h> that do
 // not define this for clang.
-#ifdef __cplusplus
-#define __CORRECT_ISO_CPP_WCHAR_H_PROTO
-#endif
-
-#  if __has_include_next(<wchar.h>)
+#    ifdef __cplusplus
+#      define __CORRECT_ISO_CPP_WCHAR_H_PROTO
+#    endif
 #    include_next <wchar.h>
 #  else
 #    include <__mbstate_t.h> // make sure we have mbstate_t regardless of the existence of <wchar.h>