Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -13523,7 +13523,8 @@
     // If this is an undefined enum, warn.
     if (TUK != TUK_Definition && !Invalid) {
       TagDecl *Def;
-      if ((getLangOpts().CPlusPlus11 || getLangOpts().ObjC2) &&
+      if (!EnumUnderlyingIsImplicit &&
+          (getLangOpts().CPlusPlus11 || getLangOpts().ObjC2) &&
           cast<EnumDecl>(New)->isFixed()) {
         // C++0x: 7.2p2: opaque-enum-declaration.
         // Conflicts are diagnosed above. Do nothing.
Index: test/SemaCXX/MicrosoftCompatibility-cxx98.cpp
===================================================================
--- test/SemaCXX/MicrosoftCompatibility-cxx98.cpp
+++ test/SemaCXX/MicrosoftCompatibility-cxx98.cpp
@@ -1,23 +0,0 @@
-// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -std=c++98 -Wmicrosoft -verify -fms-compatibility -fexceptions -fcxx-exceptions
-
-
-//MSVC allows forward enum declaration
-enum ENUM; // expected-warning {{forward references to 'enum' types are a Microsoft extension}}
-ENUM *var = 0;     
-ENUM var2 = (ENUM)3;
-enum ENUM1* var3 = 0;// expected-warning {{forward references to 'enum' types are a Microsoft extension}}
-
-typedef void (*FnPtrTy)();
-void (*PR23733_1)() = static_cast<FnPtrTy>((void *)0); // expected-warning {{static_cast between pointer-to-function and pointer-to-object is a Microsoft extension}}
-void (*PR23733_2)() = FnPtrTy((void *)0);
-void (*PR23733_3)() = (FnPtrTy)((void *)0);
-void (*PR23733_4)() = reinterpret_cast<FnPtrTy>((void *)0);
-
-long function_prototype(int a);
-long (*function_ptr)(int a);
-
-void function_to_voidptr_conv() {
-  void *a1 = function_prototype;  // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
-  void *a2 = &function_prototype; // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
-  void *a3 = function_ptr;        // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
-}
Index: test/SemaCXX/MicrosoftCompatibility.cpp
===================================================================
--- test/SemaCXX/MicrosoftCompatibility.cpp
+++ test/SemaCXX/MicrosoftCompatibility.cpp
@@ -224,6 +224,15 @@
 
 }
 
+//MSVC allows forward enum declaration
+enum ENUM; // expected-warning {{forward references to 'enum' types are a Microsoft extension}}
+ENUM *var = 0;     
+ENUM var2 = (ENUM)3;
+enum ENUM1* var3 = 0;// expected-warning {{forward references to 'enum' types are a Microsoft extension}}
+
+enum ENUM1 { kA };
+enum ENUM1;  // This way round is fine.
+
 enum ENUM2 {
 	ENUM2_a = (enum ENUM2) 4,
 	ENUM2_b = 0x9FFFFFFF, // expected-warning {{enumerator value is not representable in the underlying type 'int'}}
@@ -269,3 +278,18 @@
   f(0xffffffffffffffffi64);
 }
 }
+
+typedef void (*FnPtrTy)();
+void (*PR23733_1)() = static_cast<FnPtrTy>((void *)0); // expected-warning {{static_cast between pointer-to-function and pointer-to-object is a Microsoft extension}}
+void (*PR23733_2)() = FnPtrTy((void *)0);
+void (*PR23733_3)() = (FnPtrTy)((void *)0);
+void (*PR23733_4)() = reinterpret_cast<FnPtrTy>((void *)0);
+
+long function_prototype(int a);
+long (*function_ptr)(int a);
+
+void function_to_voidptr_conv() {
+  void *a1 = function_prototype;  // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
+  void *a2 = &function_prototype; // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
+  void *a3 = function_ptr;        // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
+}