diff --git a/win/vncviewer/DesktopWindow.cxx b/win/vncviewer/DesktopWindow.cxx
index 49b6c3f..d60ff8f 100644
--- a/win/vncviewer/DesktopWindow.cxx
+++ b/win/vncviewer/DesktopWindow.cxx
@@ -1,4 +1,5 @@
 /* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
+ * Copyright (C) 2010 D. R. Commander.  All Rights Reserved.
  * 
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -63,10 +64,10 @@
 LRESULT CALLBACK DesktopWindowProc(HWND wnd, UINT msg, WPARAM wParam, LPARAM lParam) {
   LRESULT result = 0;
   if (msg == WM_CREATE)
-    SetWindowLong(wnd, GWL_USERDATA, (long)((CREATESTRUCT*)lParam)->lpCreateParams);
+    SetWindowLongPtr(wnd, GWLP_USERDATA, (LONG_PTR)((CREATESTRUCT*)lParam)->lpCreateParams);
   else if (msg == WM_DESTROY)
-    SetWindowLong(wnd, GWL_USERDATA, 0);
-  DesktopWindow* _this = (DesktopWindow*) GetWindowLong(wnd, GWL_USERDATA);
+    SetWindowLongPtr(wnd, GWLP_USERDATA, 0);
+  DesktopWindow* _this = (DesktopWindow*) GetWindowLongPtr(wnd, GWLP_USERDATA);
   if (!_this) {
     vlog.info("null _this in %x, message %u", wnd, msg);
     return rfb::win32::SafeDefWindowProc(wnd, msg, wParam, lParam);
@@ -133,10 +134,10 @@
 LRESULT CALLBACK FrameProc(HWND wnd, UINT msg, WPARAM wParam, LPARAM lParam) {
   LRESULT result = 0;
   if (msg == WM_CREATE)
-    SetWindowLong(wnd, GWL_USERDATA, (long)((CREATESTRUCT*)lParam)->lpCreateParams);
+    SetWindowLongPtr(wnd, GWLP_USERDATA, (LONG_PTR)((CREATESTRUCT*)lParam)->lpCreateParams);
   else if (msg == WM_DESTROY)
-    SetWindowLong(wnd, GWL_USERDATA, 0);
-  DesktopWindow* _this = (DesktopWindow*) GetWindowLong(wnd, GWL_USERDATA);
+    SetWindowLongPtr(wnd, GWLP_USERDATA, 0);
+  DesktopWindow* _this = (DesktopWindow*) GetWindowLongPtr(wnd, GWLP_USERDATA);
   if (!_this) {
     vlog.info("null _this in %x, message %u", wnd, msg);
     return rfb::win32::SafeDefWindowProc(wnd, msg, wParam, lParam);