diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -403,6 +403,11 @@
     Builder.defineMacro("__STDCPP_DEFAULT_NEW_ALIGNMENT__",
                         Twine(TI.getNewAlign() / TI.getCharWidth()) +
                             TI.getTypeConstantSuffix(TI.getSizeType()));
+
+    //   -- __STDCPP_­THREADS__
+    //      Defined, and has the value integer literal 1, if and only if a
+    //      program can have more than one thread of execution.
+    Builder.defineMacro("__STDCPP_­THREADS__", "1");
   }
 
   // In C11 these are environment macros. In C++11 they are only defined