Can't use string ("1") as a subroutine ref while "strict refs" in use at $HOME/local/perl/lib/perl5/site_perl/5.12.3/Parallel/ForkManager.pm line 561 (#1)

(F) Only hard references are allowed by "strict refs".  Symbolic references are disallowed.  See perlref.

##</code><code>##

use strict;
use warnings;
use diagnostics;
use Parallel::ForkManager;

my $pm = new Parallel::ForkManager(2);

# This works
pm->run_on_finish( sub { print "Hello!\n"; } );

# This doesn't
#sub hello { print "Hello!\n"; }
#$pm->run_on_finish( &hello );

foreach my $child ( 0 .. 4 ) {
    my $pid = $pm->start and next;
	
    $pm->finish;
}

$pm->wait_all_children;