You could create your own "bytes" pragma for older versions, so that you don't get any errors while executing with these older versions of Perl.

BEGIN {
    unless (eval {require bytes}) {
        $INC{'bytes.pm'} = 1;
        eval "sub bytes::unimport{ undef }"; # 5.00503 doesn't inherit
+ UNIVERSAL::unimport
    }
}

use bytes;  # always works

no bytes;   # also always works  ;-)
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Liz