diff --git a/include/llvm/System/Mutex.h b/include/llvm/System/Mutex.h
index 16e898c2ded..8b5078d16d6 100644
--- a/include/llvm/System/Mutex.h
+++ b/include/llvm/System/Mutex.h
@@ -66,14 +66,14 @@ namespace llvm
     /// @name Platform Dependent Data
     /// @{
     private:
-        void* data_; ///< We don't know what the data will be
+      void* data_; ///< We don't know what the data will be
 
     /// @}
     /// @name Do Not Implement
     /// @{
     private: 
-	Mutex(const Mutex & original);
-	void operator=(const Mutex &);
+	    Mutex(const Mutex & original);
+	    void operator=(const Mutex &);
     /// @}
     };
   }
diff --git a/lib/System/Mutex.cpp b/lib/System/Mutex.cpp
index 2a151976913..4ec5af302f9 100644
--- a/lib/System/Mutex.cpp
+++ b/lib/System/Mutex.cpp
@@ -14,15 +14,16 @@
 #include "llvm/System/Mutex.h"
 #include "llvm/Config/config.h"
 
-namespace llvm {
-using namespace sys;
-
 //===----------------------------------------------------------------------===//
 //=== WARNING: Implementation here must contain only TRULY operating system
 //===          independent code.
 //===----------------------------------------------------------------------===//
 
 #if defined(HAVE_PTHREAD_H) && defined(HAVE_PTHREAD_MUTEX_LOCK)
+
+namespace llvm {
+using namespace sys;
+
 #include <cassert>
 #include <pthread.h>
 #include <stdlib.h>
@@ -132,6 +133,7 @@ Mutex::tryacquire()
 }
 
 }
+
 #elif defined(LLVM_ON_UNIX)
 #include "Unix/Mutex.inc"
 #elif defined( LLVM_ON_WIN32)
diff --git a/lib/System/Win32/Mutex.inc b/lib/System/Win32/Mutex.inc
index d6acb2352be..439ce1a401a 100644
--- a/lib/System/Win32/Mutex.inc
+++ b/lib/System/Win32/Mutex.inc
@@ -2,7 +2,7 @@
 // 
 //                     The LLVM Compiler Infrastructure
 //
-// This file was developed by Reid Spencer and is distributed under the 
+// This file was developed by Jeff Cohen and is distributed under the 
 // University of Illinois Open Source License. See LICENSE.TXT for details.
 // 
 //===----------------------------------------------------------------------===//
@@ -16,31 +16,42 @@
 //===          is guaranteed to work on *all* Win32 variants.
 //===----------------------------------------------------------------------===//
 
-namespace llvm
-{
+#include "Win32.h"
+#include "llvm/System/Mutex.h"
+
+namespace llvm {
 using namespace sys;
 
-Mutex::Mutex( bool recursive)
+Mutex::Mutex(bool /*recursive*/)
 {
+  data_ = new CRITICAL_SECTION;
+  InitializeCriticalSection((LPCRITICAL_SECTION)data_);
 }
 
 Mutex::~Mutex()
 {
+  DeleteCriticalSection((LPCRITICAL_SECTION)data_);
+  data_ = 0;
 }
 
 bool 
 Mutex::acquire()
 {
+  EnterCriticalSection((LPCRITICAL_SECTION)data_);
+  return true;
 }
 
 bool 
 Mutex::release()
 {
+  LeaveCriticalSection((LPCRITICAL_SECTION)data_);
+  return true;
 }
 
 bool 
-Mutex::tryacquire( void )
+Mutex::tryacquire()
 {
+  return TryEnterCriticalSection((LPCRITICAL_SECTION)data_);
 }
 
 }
diff --git a/lib/System/Win32/Win32.h b/lib/System/Win32/Win32.h
index 6cda8c675fe..7ed10471de1 100644
--- a/lib/System/Win32/Win32.h
+++ b/lib/System/Win32/Win32.h
@@ -2,20 +2,23 @@
 //
 //                     The LLVM Compiler Infrastructure
 //
-// This file was developed by Reid Spencer and is distributed under the
+// This file was developed by Jeff Cohen and is distributed under the
 // University of Illinois Open Source License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
-// This file defines things specific to Unix implementations.
+// This file defines things specific to Win32 implementations.
 //
 //===----------------------------------------------------------------------===//
 
 //===----------------------------------------------------------------------===//
-//=== WARNING: Implementation here must contain only generic UNIX code that
-//===          is guaranteed to work on all UNIX variants.
+//=== WARNING: Implementation here must contain only generic Win32 code that
+//===          is guaranteed to work on *all* Win32 variants.
 //===----------------------------------------------------------------------===//
 
+// Require at least Windows 2000 API.
+#define _WIN32_WINNT 0x0500
+
 #include "llvm/Config/config.h"     // Get autoconf configuration settings
 #include "windows.h"
 #include <cassert>
diff --git a/win32/System/System.vcproj b/win32/System/System.vcproj
index 2f03809667f..c14f7cf937d 100644
--- a/win32/System/System.vcproj
+++ b/win32/System/System.vcproj
@@ -116,6 +116,9 @@
 			<File
 				RelativePath="..\..\lib\System\Memory.cpp">
 			</File>
+			<File
+				RelativePath="..\..\lib\System\Mutex.cpp">
+			</File>
 			<File
 				RelativePath="..\..\lib\System\Path.cpp">
 			</File>
@@ -145,6 +148,9 @@
 			<File
 				RelativePath="..\..\include\llvm\System\Memory.h">
 			</File>
+			<File
+				RelativePath="..\..\include\llvm\System\Mutex.h">
+			</File>
 			<File
 				RelativePath="..\..\include\llvm\System\Path.h">
 			</File>
@@ -173,6 +179,9 @@
 			<File
 				RelativePath="..\..\lib\System\Win32\Memory.inc">
 			</File>
+			<File
+				RelativePath="..\..\lib\System\Win32\Mutex.inc">
+			</File>
 			<File
 				RelativePath="..\..\lib\System\Win32\Path.inc">
 			</File>