When running a script using strict, I am getting the warning:

main::usage() called too early to check prototype at X:\bin\backup.pl 
+line 18.
main::usage() called too early to check prototype at X:\bin\backup.pl 
+line 26.
[download]

Does perl require function prototypes similiar to C under certain circumstances?

Code that produced the error (for reference):

#!/usr/bin/perl -w
#
# backup - perform a daily or weekly backup of a preset list of files.
#    by Micah Valine (mvaline@buffnet.net)
#

use strict;

### program settings ###
my $daily_backup_dir = "X:\\backup\\daily\\";
my $weekly_backup_dir = "X:\backup\\weekly\\";
my $filelist = "X:\\.backup";
my $daily_flag = "d";
my $weekly_flag = "w";
my $target;

### process arguments ###
usage() if (!@ARGV);
if ($ARGV[0] eq "-d") {
    $target = $daily_flag;
}
elsif ($ARGV[0] eq "-w") {
    $target = $weekly_flag;
}
else {
    usage();
}

### usage: print usage information and die ###
sub usage()
{
    print STDERR << "END_USAGE";
usage: backup [-dw]
         -d performs a daily backup
         -w performs a weekly backup
END_USAGE
    exit 1;
}
[download]

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