Index: clang/lib/Basic/Targets/OSTargets.cpp
===================================================================
--- clang/lib/Basic/Targets/OSTargets.cpp
+++ clang/lib/Basic/Targets/OSTargets.cpp
@@ -181,7 +181,9 @@
       Builder.defineMacro("_HAS_CHAR16_T_LANGUAGE_SUPPORT", Twine(1));
 
     if (Opts.isCompatibleWithMSVC(LangOptions::MSVC2015)) {
-      if (Opts.CPlusPlus20)
+      if (Opts.CPlusPlus2b)
+        Builder.defineMacro("_MSVC_LANG", "202004L");
+      else if (Opts.CPlusPlus20)
         Builder.defineMacro("_MSVC_LANG", "202002L");
       else if (Opts.CPlusPlus17)
         Builder.defineMacro("_MSVC_LANG", "201703L");
Index: clang/test/Preprocessor/predefined-win-macros.c
===================================================================
--- clang/test/Preprocessor/predefined-win-macros.c
+++ clang/test/Preprocessor/predefined-win-macros.c
@@ -45,9 +45,14 @@
 // CHECK-MS-NOT: GXX
 
 // RUN: %clang_cc1 %s -x c++ -E -dM -triple i686-pc-win32 -fms-extensions -fms-compatibility \
-// RUN:     -fms-compatibility-version=19.00 -std=c++20 -o - | FileCheck -match-full-lines %s --check-prefix=CHECK-MS-CPP2A
-// CHECK-MS-CPP2A: #define _MSC_VER 1900
-// CHECK-MS-CPP2A: #define _MSVC_LANG 202002L
+// RUN:     -fms-compatibility-version=19.00 -std=c++20 -o - | FileCheck -match-full-lines %s --check-prefix=CHECK-MS-CPP20
+// CHECK-MS-CPP20: #define _MSC_VER 1900
+// CHECK-MS-CPP20: #define _MSVC_LANG 202002L
+
+// RUN: %clang_cc1 %s -x c++ -E -dM -triple i686-pc-win32 -fms-extensions -fms-compatibility \
+// RUN:     -fms-compatibility-version=19.00 -std=c++2b -o - | FileCheck -match-full-lines %s --check-prefix=CHECK-MS-CPP2B
+// CHECK-MS-CPP2B: #define _MSC_VER 1900
+// CHECK-MS-CPP2B: #define _MSVC_LANG 202004L
 
 // RUN: %clang_cc1 -triple i386-windows %s -E -dM -o - \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-X86-WIN