diff --git a/clang/lib/Frontend/InitPreprocessor.cpp.orig        b/clang/lib/Frontend/InitPreprocessor.cpp    
--- a/clang/lib/Frontend/InitPreprocessor.cpp.orig       	
+++ b/clang/lib/Frontend/InitPreprocessor.cpp    	
@@ -1019,6 +1019,9 @@

   Builder.defineMacro("__USER_LABEL_PREFIX__", TI.getUserLabelPrefix());

+  if (LangOpts.FastMath || !LangOpts.MathErrno)
+    Builder.defineMacro("__NO_MATH_ERRNO__");
+
   if (LangOpts.FastMath || LangOpts.FiniteMathOnly)
     Builder.defineMacro("__FINITE_MATH_ONLY__", "1");
   else