diff --git a/reactos/subsystems/win32/win32k/include/ntuser.h b/reactos/subsystems/win32/win32k/include/ntuser.h
index eb71cc711fc..256aa6b85eb 100644
--- a/reactos/subsystems/win32/win32k/include/ntuser.h
+++ b/reactos/subsystems/win32/win32k/include/ntuser.h
@@ -1,58 +1,23 @@
 #ifndef _WIN32K_NTUSER_H
 #define _WIN32K_NTUSER_H
 
-
-extern char* _file;
-extern DWORD _line;
-extern DWORD _locked;
-
-extern FAST_MUTEX UserLock;
-
 #define DECLARE_RETURN(type) type _ret_
 #define RETURN(value) { _ret_ = value; goto _cleanup_; }
 #define CLEANUP /*unreachable*/ ASSERT(FALSE); _cleanup_
 #define END_CLEANUP return _ret_;
 
 
-#define UserEnterCo() UserEnterExclusive()
-#define UserLeaveCo() UserLeave()
-
-#define UserEnterShared() UserEnterExclusive()
-
-#define UserEnterExclusive() \
-{ \
-  /* DPRINT1("try xlock, %s, %i (%i)\n",__FILE__,__LINE__, _locked);*/ \
-   if (UserLock.Owner == KeGetCurrentThread()){ \
-      DPRINT1("file %s, line %i\n",_file, _line); \
-      ASSERT(FALSE); \
-   }  \
-   UUserEnterExclusive(); \
-   ASSERT(InterlockedIncrement((PLONG)(&_locked)) == 1 /*> 0*/); \
-   _file = __FILE__; _line = __LINE__; \
-  /* DPRINT("got lock, %s, %i (%i)\n",__FILE__,__LINE__, _locked);*/ \
-}
-
-#define UserLeave() \
-{ \
-   ASSERT(InterlockedDecrement((PLONG)(&_locked)) == 0/*>= 0*/); \
-   /*DPRINT("unlock, %s, %i (%i)\n",__FILE__,__LINE__, _locked);*/ \
-   if (UserLock.Owner != KeGetCurrentThread()) { \
-     DPRINT1("file %s, line %i\n",_file, _line); \
-     ASSERT(FALSE); \
-   } \
-   _file = __FILE__; _line = __LINE__; \
-   UUserLeave(); \
-}
- 
+#define UserEnterCo UserEnterExclusive
+#define UserLeaveCo UserLeave
 
 
 NTSTATUS FASTCALL InitUserImpl(VOID);
-VOID FASTCALL UninitUser(VOID);
-VOID FASTCALL UUserEnterShared(VOID);
-VOID FASTCALL UUserEnterExclusive(VOID);
-VOID FASTCALL UUserLeave(VOID);
+VOID FASTCALL CleanupUserImpl(VOID);
+VOID FASTCALL UserEnterShared(VOID);
+VOID FASTCALL UserEnterExclusive(VOID);
+VOID FASTCALL UserLeave(VOID);
 BOOL FASTCALL UserIsEntered();
-
+BOOL FASTCALL UserIsEnteredExclusive();
 
 
 #endif /* _WIN32K_NTUSER_H */
diff --git a/reactos/subsystems/win32/win32k/ntuser/class.c b/reactos/subsystems/win32/win32k/ntuser/class.c
index 1e4be17713c..d77b115321a 100644
--- a/reactos/subsystems/win32/win32k/ntuser/class.c
+++ b/reactos/subsystems/win32/win32k/ntuser/class.c
@@ -220,8 +220,8 @@ IntGetClassWndProc(IN PWINDOWCLASS Class,
                    IN BOOL Ansi,
                    IN BOOL UseCallProc2)
 {
-    /* FIXME - assert for exclusive lock! */
-
+    ASSERT(UserIsEnteredExclusive() == TRUE);
+    
     if (Class->System)
     {
         return (Ansi ? Class->WndProcExtra : Class->WndProc);
diff --git a/reactos/subsystems/win32/win32k/ntuser/ntuser.c b/reactos/subsystems/win32/win32k/ntuser/ntuser.c
index ca45604dd48..0ddba1eb5bc 100644
--- a/reactos/subsystems/win32/win32k/ntuser/ntuser.c
+++ b/reactos/subsystems/win32/win32k/ntuser/ntuser.c
@@ -33,25 +33,16 @@
 #define NDEBUG
 #include <debug.h>
 
-
-FAST_MUTEX UserLock;
-
-char* _file;
-DWORD _line;
-DWORD _locked=0;
+ERESOURCE UserLock;
 
 /* FUNCTIONS **********************************************************/
 
 
 NTSTATUS FASTCALL InitUserImpl(VOID)
 {
-   //PVOID mem;
    NTSTATUS Status;
 
-   //   DPRINT("Enter InitUserImpl\n");
-   //   ExInitializeResourceLite(&UserLock);
-
-   ExInitializeFastMutex(&UserLock);
+   ExInitializeResourceLite(&UserLock);
 
    if (!ObmCreateHandleTable())
    {
@@ -75,41 +66,31 @@ RETURN
 */
 BOOL FASTCALL UserIsEntered()
 {
-   return (UserLock.Owner == KeGetCurrentThread());
+   return ExIsResourceAcquiredExclusiveLite(&UserLock) 
+      || ExIsResourceAcquiredSharedLite(&UserLock);
 }
 
-
-VOID FASTCALL CleanupUser(VOID)
+BOOL FASTCALL UserIsEnteredExclusive()
 {
-   //   ExDeleteResourceLite(&UserLock);
+   return ExIsResourceAcquiredExclusiveLite(&UserLock);
 }
 
-VOID FASTCALL UUserEnterShared(VOID)
+VOID FASTCALL CleanupUserImpl(VOID)
 {
-   //   DPRINT("Enter IntLockUserShared\n");
-   //   KeDumpStackFrames((PULONG)__builtin_frame_address(0));
-   //DPRINT("%x\n",__builtin_return_address(0));
-   //   KeEnterCriticalRegion();
-   //   ExAcquireResourceSharedLite(&UserLock, TRUE);
-   ExEnterCriticalRegionAndAcquireFastMutexUnsafe(&UserLock);
+   ExDeleteResourceLite(&UserLock);
 }
 
-VOID FASTCALL UUserEnterExclusive(VOID)
+VOID FASTCALL UserEnterShared(VOID)
 {
-   //   DPRINT("Enter UserEnterExclusive\n");
-   //   KeDumpStackFrames((PULONG)__builtin_frame_address(0));
-   //DPRINT("%x\n",__builtin_return_address(0));
-   //   KeEnterCriticalRegion();
-   //   ExAcquireResourceExclusiveLite(&UserLock, TRUE);
-   ExEnterCriticalRegionAndAcquireFastMutexUnsafe(&UserLock);
+   ExAcquireResourceSharedLite(&UserLock, TRUE);
 }
 
-VOID FASTCALL UUserLeave(VOID)
+VOID FASTCALL UserEnterExclusive(VOID)
 {
-   //   DPRINT("Enter UserLeave\n");
-   //   KeDumpStackFrames((PULONG)__builtin_frame_address(0));
-   //DPRINT("%x\n",__builtin_return_address(0));
-   //  ExReleaseResourceLite(&UserLock);
-   //   KeLeaveCriticalRegion();
-   ExReleaseFastMutexUnsafeAndLeaveCriticalRegion(&UserLock);
+   ExAcquireResourceExclusiveLite(&UserLock, TRUE);
+}
+
+VOID FASTCALL UserLeave(VOID)
+{
+   ExReleaseResourceLite(&UserLock);
 }