def _hostname_matches(cert_pattern, actual_hostname):
    """
    :type cert_pattern: `bytes`
    :type actual_hostname: `bytes`

    :return: `True` if *cert_pattern* matches *actual_hostname*, else `False`.
    :rtype: `bool`
    """
    if b"*" in cert_pattern:
        cert_head, cert_tail = cert_pattern.split(b".", 1)
        actual_head, actual_tail = actual_hostname.split(b".", 1)
        if cert_tail != actual_tail:
            return False
        # No patterns for IDNA
        if actual_head.startswith(b"xn--"):
            return False

        return cert_head == b"*" or cert_head == actual_head
    else:
        return cert_pattern == actual_hostname