blocklistd.conf blocking an ipv6 /48 subnet

I understand that the blocklistd.conf syntax for blocking an ipv4 subnet is the following:

     [remote]
     * stream tcp * =/24 = =

Presumably, there is something similar for blocking an ipv6 subnet.  I have tried replacing the address (field 1) with [*] and the name (field 5) with =/48, but that seems to block ipv4 subnets with a mask of /48.

What is the syntax for blocking a ipv6 /48 subnet?

Thanks for your help.

Cheers,
Brook