Cannot make a blessed object readonly

[exodist]

use strict;
use warnings;

use ReadonlyX;

my $x = bless({}, "Foo::Bar");

Readonly::Hash(%$x, %$x);

The above code works fine with Readonly. It does not work with ReadonlyX

We do not know what to do with Foo::Bar at xxx.pl line 8.

With regular Readonly I am able to use this to make an entire object Readonly.