Win32: fixed wrong type cast. GetQueuedCompletionStatus() document on MSDN says the following signature: http://msdn.microsoft.com/en-us/library/windows/desktop/aa364986.aspx BOOL WINAPI GetQueuedCompletionStatus( _In_ HANDLE CompletionPort, _Out_ LPDWORD lpNumberOfBytes, _Out_ PULONG_PTR lpCompletionKey, _Out_ LPOVERLAPPED *lpOverlapped, _In_ DWORD dwMilliseconds ); In the latest specification, the type of the third argument (lpCompletionKey) is PULONG_PTR not LPDWORD.