Index: clang/lib/Basic/Targets/OSTargets.cpp
===================================================================
--- clang/lib/Basic/Targets/OSTargets.cpp
+++ clang/lib/Basic/Targets/OSTargets.cpp
@@ -201,6 +201,7 @@
   }
 
   Builder.defineMacro("_INTEGRAL_MAX_BITS", "64");
+  Builder.defineMacro("__STDC_NO_THREADS__");
 }
 
 void addWindowsDefines(const llvm::Triple &Triple, const LangOptions &Opts,
Index: clang/test/Preprocessor/init.c
===================================================================
--- clang/test/Preprocessor/init.c
+++ clang/test/Preprocessor/init.c
@@ -192,6 +192,7 @@
 //
 // MSEXT-NOT:#define __STDC__
 // MSEXT:#define _INTEGRAL_MAX_BITS 64
+// MSEXT:#define __STDC_NO_THREADS__ 1
 // MSEXT-NOT:#define _NATIVE_WCHAR_T_DEFINED 1
 // MSEXT-NOT:#define _WCHAR_T_DEFINED 1
 //