use strict;
use warnings;
package MyMod;
use Exporter ();
use MyMod::db;

use vars qw (@EXPORT @EXPORT_OK);
use constant MYMOD_DEFAULT => 1;
BEGIN {
    @EXPORT = (qw(MYMOD_DEFAULT));
    #@EXPORT_OK = (qw(MYMOD_DEFAULT));
};
1;

use strict;
use warnings;
package MyMod::db;
# I also tried use MyMod qw(MYMOD_DEFAULT) when constant was
# in EXPORT_OK and not EXPORT.
use base qw(MyMod);
sub fred {
        print "hello" if (MYMOD_DEFAULT);
}
1;