diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1695,9 +1695,6 @@
 def ext_missing_exception_specification : ExtWarn<
   err_missing_exception_specification.Text>,
   InGroup<DiagGroup<"missing-exception-spec">>;
-def ext_ms_missing_exception_specification : ExtWarn<
-  err_missing_exception_specification.Text>,
-  InGroup<MicrosoftExceptionSpec>;
 def err_noexcept_needs_constant_expression : Error<
   "argument to noexcept specifier must be a constant expression">;
 def err_exception_spec_not_parsed : Error<
diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -391,9 +391,8 @@
         NewProto->getExtProtoInfo().withExceptionSpec(ESI)));
   }
 
-  if (getLangOpts().MSVCCompat && ESI.Type != EST_DependentNoexcept) {
-    // Allow missing exception specifications in redeclarations as an extension.
-    DiagID = diag::ext_ms_missing_exception_specification;
+  if (getLangOpts().MSVCCompat && isDynamicExceptionSpec(ESI.Type)) {
+    DiagID = diag::ext_missing_exception_specification;
     ReturnValueOnError = false;
   } else if (New->isReplaceableGlobalAllocationFunction() &&
              ESI.Type != EST_DependentNoexcept) {
@@ -402,6 +401,10 @@
     DiagID = diag::ext_missing_exception_specification;
     ReturnValueOnError = false;
   } else if (ESI.Type == EST_NoThrow) {
+    // Don't emit any warning for missing 'nothrow' in MSVC.
+    if (getLangOpts().MSVCCompat) {
+      return false;
+    }
     // Allow missing attribute 'nothrow' in redeclarations, since this is a very
     // common omission.
     DiagID = diag::ext_missing_exception_specification;
diff --git a/clang/test/SemaCXX/MicrosoftCompatibility.cpp b/clang/test/SemaCXX/MicrosoftCompatibility.cpp
--- a/clang/test/SemaCXX/MicrosoftCompatibility.cpp
+++ b/clang/test/SemaCXX/MicrosoftCompatibility.cpp
@@ -2,6 +2,8 @@
 // RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -std=c++11 -Wmicrosoft -verify -fms-compatibility -fexceptions -fcxx-exceptions -fms-compatibility-version=19.27
 // RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -std=c++11 -Wmicrosoft -verify -fms-compatibility -fexceptions -fcxx-exceptions -fms-compatibility-version=19.00
 // RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -std=c++11 -Wmicrosoft -verify -fms-compatibility -fexceptions -fcxx-exceptions -fms-compatibility-version=18.00
+// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -std=c++17 -Wmicrosoft -verify -fms-compatibility -fexceptions -fcxx-exceptions
+
 
 #if defined(_HAS_CHAR16_T_LANGUAGE_SUPPORT) && _HAS_CHAR16_T_LANGUAGE_SUPPORT
 char16_t x;
@@ -350,6 +352,7 @@
 void foo(); // expected-note {{previous declaration}}
 void foo() throw(); // expected-warning {{exception specification in declaration does not match previous declaration}}
 
+#if __cplusplus < 201703L
 void r6() throw(...); // expected-note {{previous declaration}}
 void r6() throw(int); // expected-warning {{exception specification in declaration does not match previous declaration}}
 
@@ -362,6 +365,7 @@
   virtual void f2() throw(...);
   virtual void f3();
 };
+#endif
 
 class A {
   virtual ~A() throw();
@@ -377,14 +381,14 @@
 #endif
 };
 
-}
+void f4() throw(); // expected-note {{previous declaration is here}}
+void f4() {}       // expected-warning {{'f4' is missing exception specification 'throw()'}}
 
-namespace PR25265 {
-struct S {
-  int fn() throw(); // expected-note {{previous declaration is here}}
-};
+__declspec(nothrow) void f5();
+void f5() {}
 
-int S::fn() { return 0; } // expected-warning {{is missing exception specification}}
+void f6() noexcept; // expected-note {{previous declaration is here}}
+void f6() {}        // expected-error {{'f6' is missing exception specification 'noexcept'}}
 }
 
 namespace PR43265 {