Index: clang/lib/Frontend/InitPreprocessor.cpp
===================================================================
--- clang/lib/Frontend/InitPreprocessor.cpp
+++ clang/lib/Frontend/InitPreprocessor.cpp
@@ -1039,6 +1039,9 @@

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

+  if (LangOpts.MathErrno)
+    Builder.defineMacro("__NO_MATH_ERRNO__");
+
   if (LangOpts.FastMath || LangOpts.FiniteMathOnly)
     Builder.defineMacro("__FINITE_MATH_ONLY__", "1");
   else
Index: clang/test/Preprocessor/predefined-macros.c
===================================================================
--- clang/test/Preprocessor/predefined-macros.c
+++ clang/test/Preprocessor/predefined-macros.c
@@ -59,8 +59,17 @@
 // RUN: %clang_cc1 %s -E -dM -ffast-math -o - \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-FAST-MATH
 // CHECK-FAST-MATH: #define __FAST_MATH__ 1
+// CHECK-FAST-MATH: #define __NO_MATH_ERRNO__ 1
 // CHECK-FAST-MATH: #define __FINITE_MATH_ONLY__ 1
 //
+// RUN: %clang_cc1 %s -E -dM -fmath-errno -o - \
+// RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-MATH-ERRNO
+// CHECK-MATH-ERRNO-NOT: __NO_MATH_ERRNO__
+//
+// RUN: %clang %s -E -dM -fno-math-errno -o - \
+// RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-NO-MATH-ERRNO
+// CHECK-NO-MATH-ERRNO: #define __NO_MATH_ERRNO__ 1
+//
 // RUN: %clang_cc1 %s -E -dM -ffinite-math-only -o - \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-FINITE-MATH-ONLY
 // CHECK-FINITE-MATH-ONLY: #define __FINITE_MATH_ONLY__ 1