Index: lib/Basic/Targets/AArch64.cpp
===================================================================
--- lib/Basic/Targets/AArch64.cpp
+++ lib/Basic/Targets/AArch64.cpp
@@ -474,7 +474,6 @@
 void MicrosoftARM64TargetInfo::getVisualStudioDefines(
     const LangOptions &Opts, MacroBuilder &Builder) const {
   WindowsTargetInfo<AArch64leTargetInfo>::getVisualStudioDefines(Opts, Builder);
-  Builder.defineMacro("_WIN32", "1");
   Builder.defineMacro("_WIN64", "1");
   Builder.defineMacro("_M_ARM64", "1");
 }
@@ -494,10 +493,9 @@
 void MinGWARM64TargetInfo::getTargetDefines(const LangOptions &Opts,
                                             MacroBuilder &Builder) const {
   WindowsTargetInfo::getTargetDefines(Opts, Builder);
-  Builder.defineMacro("_WIN32", "1");
+  DefineStd(Builder, "WIN32", Opts);
+  DefineStd(Builder, "WINNT", Opts);
   Builder.defineMacro("_WIN64", "1");
-  Builder.defineMacro("WIN32", "1");
-  Builder.defineMacro("WIN64", "1");
   addMinGWDefines(Opts, Builder);
 }
 
Index: lib/Basic/Targets/X86.h
===================================================================
--- lib/Basic/Targets/X86.h
+++ lib/Basic/Targets/X86.h
@@ -726,7 +726,6 @@
   void getTargetDefines(const LangOptions &Opts,
                         MacroBuilder &Builder) const override {
     WindowsX86_64TargetInfo::getTargetDefines(Opts, Builder);
-    DefineStd(Builder, "WIN64", Opts);
     Builder.defineMacro("__MINGW64__");
     addMinGWDefines(Opts, Builder);
 
Index: test/Preprocessor/predefined-macros.c
===================================================================
--- test/Preprocessor/predefined-macros.c
+++ test/Preprocessor/predefined-macros.c
@@ -200,12 +200,20 @@
 // CHECK-ARM64-WIN: #define _WIN32 1
 // CHECK-ARM64-WIN: #define _WIN64 1
 
+// RUN: %clang_cc1 -triple x86_64-windows-gnu %s -E -dM -o - \
+// RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-AMD64-MINGW
+
+// CHECK-AMD64-MINGW: #define WIN32 1
+// CHECK-AMD64-MINGW: #define WINNT 1
+// CHECK-AMD64-MINGW: #define _WIN32 1
+// CHECK-AMD64-MINGW: #define _WIN64 1
+
 // RUN: %clang_cc1 -triple aarch64-windows-gnu %s -E -dM -o - \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-ARM64-MINGW
 
 // CHECK-ARM64-MINGW-NOT: #define _M_ARM64 1
 // CHECK-ARM64-MINGW: #define WIN32 1
-// CHECK-ARM64-MINGW: #define WIN64 1
+// CHECK-ARM64-MINGW: #define WINNT 1
 // CHECK-ARM64-MINGW: #define _WIN32 1
 // CHECK-ARM64-MINGW: #define _WIN64 1
 // CHECK-ARM64-MINGW: #define __aarch64__ 1