No: on Windows it is a real WINAPI handle. And those are of course not portable. E.g. GetWindowLongPtr and such can not be used on other platforms and the format / type of the handle may differ (is different) on other platforms. In this case it is the use of the handle that triggers the warning. If you would use Tform.handle in the same manner, you will get the same warning. Under windows all handles are system.THandle which is on windows a windows specific handle.