Why does StreamReader.ReadLine throw OutOfMemoryException?

Can anyone tell me why the last line here throws OOM exception?

        byte[] buffer = new byte[1];
        buffer[0] = 239;
        MemoryStream ms = new MemoryStream(buffer);
        StreamReader sr = new StreamReader(ms);
        string l1 = sr.ReadLine();
        string l2 = sr.ReadLine();