diff --git a/reactos/subsystems/win32/win32k/ntuser/timer.c b/reactos/subsystems/win32/win32k/ntuser/timer.c
index a1da2d64314..1c34ab751d5 100644
--- a/reactos/subsystems/win32/win32k/ntuser/timer.c
+++ b/reactos/subsystems/win32/win32k/ntuser/timer.c
@@ -279,7 +279,9 @@ PostTimerMessages(PWINDOW_OBJECT Window)
 
   if (!pTmr) return FALSE;
 
-  if (Window && (int)Window != 1)
+  ASSERT(Window);
+
+  if (Window && ((ULONG_PTR)Window != 1))
   {
      if (!Window->Wnd) return FALSE;
   }
@@ -294,6 +296,7 @@ PostTimerMessages(PWINDOW_OBJECT Window)
           (pTmr->pti == pti) &&
           (pTmr->pWnd == Window))
         {
+           ASSERT((ULONG_PTR)Window != 1);
            Msg.hwnd    = Window->hSelf;
            Msg.message = (pTmr->flags & TMRF_SYSTEM) ? WM_SYSTIMER : WM_TIMER;
            Msg.wParam  = (WPARAM) pTmr->nID;