#! /usr/bin/perl -w

use strict;

use Safe;

my $CODE = << 'END';

package A;

sub new {
  my($class) = @_;
  bless { }, $class;
}

package B; 

our @ISA = qw(A);

END

# If I uncomment this line, everything works.
# eval $CODE;

my $safe = Safe->new();

$safe->reval($CODE);       
warn "code - $@" if $@;
$safe->reval("B->new();"); 
warn "new - $@" if $@;