Index: libcxx/include/thread
===================================================================
--- libcxx/include/thread
+++ libcxx/include/thread
@@ -14,8 +14,6 @@
 
     thread synopsis
 
-#define __STDCPP_THREADS__ __cplusplus
-
 namespace std
 {
 
@@ -107,7 +105,9 @@
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
-#define __STDCPP_THREADS__ __cplusplus
+#ifndef __STDCPP_THREADS__
+#define __STDCPP_THREADS__ 1
+#endif
 
 #ifdef _LIBCPP_HAS_NO_THREADS
 #error <thread> is not supported on this single threaded system
Index: libcxx/test/std/thread/macro.pass.cpp
===================================================================
--- libcxx/test/std/thread/macro.pass.cpp
+++ libcxx/test/std/thread/macro.pass.cpp
@@ -10,7 +10,7 @@
 
 // <thread>
 
-// #define __STDCPP_THREADS__ __cplusplus
+// #define __STDCPP_THREADS__ 1
 
 #include <thread>
 
@@ -20,6 +20,8 @@
 {
 #ifndef __STDCPP_THREADS__
 #error __STDCPP_THREADS__ is not defined
+#elif __STDCPP_THREADS__ != 1
+#error __STDCPP_THREADS__ has the wrong value
 #endif
 
   return 0;