diff --git a/include/wx/msw/private/timer.h b/include/wx/msw/private/timer.h
index f7044e0754..7878c77a67 100644
--- a/include/wx/msw/private/timer.h
+++ b/include/wx/msw/private/timer.h
@@ -26,7 +26,7 @@ public:
     virtual bool IsRunning() const { return m_id != 0; }
 
 protected:
-    unsigned long m_id;
+    WPARAM m_id;
 };
 
 #endif // wxUSE_TIMER
diff --git a/src/msw/timer.cpp b/src/msw/timer.cpp
index 48d24f04d0..9442d09a5b 100644
--- a/src/msw/timer.cpp
+++ b/src/msw/timer.cpp
@@ -38,7 +38,7 @@
 
 // define a hash containing all the timers: it is indexed by timer id and
 // contains the corresponding timer
-WX_DECLARE_HASH_MAP(unsigned long, wxMSWTimerImpl *, wxIntegerHash, wxIntegerEqual,
+WX_DECLARE_HASH_MAP(WPARAM, wxMSWTimerImpl *, wxIntegerHash, wxIntegerEqual,
                     wxTimerMap);
 
 // instead of using a global here, wrap it in a static function as otherwise it
@@ -173,7 +173,7 @@ LRESULT APIENTRY _EXPORT wxTimerWndProc(HWND hWnd, UINT message,
 {
     if ( message == WM_TIMER )
     {
-        wxTimerMap::iterator node = TimerMap().find((unsigned long)wParam);
+        wxTimerMap::iterator node = TimerMap().find(wParam);
 
         wxCHECK_MSG( node != TimerMap().end(), 0, wxT("bogus timer id in wxTimerProc") );