diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 0d97709..dfc46f4 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -453,6 +453,8 @@
   }
   if (LangOpts.SizedDeallocation)
     Builder.defineMacro("__cpp_sized_deallocation", "201309");
+  if (LangOpts.ConceptsTS)
+    Builder.defineMacro("__cpp_experimental_concepts", "1");
 }
 
 static void InitializePredefinedMacros(const TargetInfo &TI,