diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index e3279c2..1f15556 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -469,6 +469,9 @@
   if (FEOpts.ProgramAction == frontend::RunAnalysis)
     Builder.defineMacro("__clang_analyzer__");
 
+  if (LangOpts.FastRelaxedMath)
+    Builder.defineMacro("__FAST_RELAXED_MATH__");
+
   // Get other target #defines.
   TI.getTargetDefines(LangOpts, Builder);
 }