Index: lib/Frontend/InitPreprocessor.cpp
===================================================================
--- lib/Frontend/InitPreprocessor.cpp	(revision 151865)
+++ lib/Frontend/InitPreprocessor.cpp	(working copy)
@@ -319,11 +319,14 @@
                       + getClangFullRepositoryVersion() + ")\"");
 #undef TOSTR
 #undef TOSTR2
-  // Currently claim to be compatible with GCC 4.2.1-5621.
-  Builder.defineMacro("__GNUC_MINOR__", "2");
-  Builder.defineMacro("__GNUC_PATCHLEVEL__", "1");
-  Builder.defineMacro("__GNUC__", "4");
-  Builder.defineMacro("__GXX_ABI_VERSION", "1002");
+  if (!LangOpts.MSCVersion) {
+    // Currently claim to be compatible with GCC 4.2.1-5621, but only if we're
+    // not compiling for MSVC compatibility
+    Builder.defineMacro("__GNUC_MINOR__", "2");
+    Builder.defineMacro("__GNUC_PATCHLEVEL__", "1");
+    Builder.defineMacro("__GNUC__", "4");
+    Builder.defineMacro("__GXX_ABI_VERSION", "1002");
+  }
 
   // Define macros for the C11 / C++11 memory orderings
   Builder.defineMacro("__ATOMIC_RELAXED", "0");
Index: test/Preprocessor/predefined-macros.c
===================================================================
--- test/Preprocessor/predefined-macros.c	(revision 151865)
+++ test/Preprocessor/predefined-macros.c	(working copy)
@@ -8,6 +8,7 @@
 // CHECK-MS: #define _M_IX86 600
 // CHECK-MS: #define _M_IX86_FP
 // CHECK-MS: #define _WIN32 1
+// CHECK-MS-NOT: #define __GNUC__
 //
 // RUN: %clang_cc1 %s -E -dM -ffast-math -o - \
 // RUN:   | FileCheck %s --check-prefix=CHECK-FAST-MATH