diff --git a/win32ss/user/ntuser/misc.c b/win32ss/user/ntuser/misc.c
index 196ea416e79..c0e332b369e 100644
--- a/win32ss/user/ntuser/misc.c
+++ b/win32ss/user/ntuser/misc.c
@@ -402,7 +402,7 @@ NtUserGetGUIThreadInfo(
       pti = PsGetCurrentThreadWin32Thread();
 
       // Validate Tread ID
-      W32Thread = IntTID2PTI((HANDLE)idThread);
+      W32Thread = IntTID2PTI((HANDLE)(DWORD_PTR)idThread);
 
       if ( !W32Thread )
       {