Use the :i specifier. Refer to Summary of Option Specifications. 
use warnings;
use strict;
use Getopt::Long;

my $arg = -1;
GetOptions('arg:i' => \$arg) or die;
print "$arg\n";

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In reply to Re: Trickery with Getopt::Long (flag option, with optional integer arg) by toolic
in thread Trickery with Getopt::Long (flag option, with optional integer arg) by stevieb

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