sub _mtime {
    my ($self, $filepath) = @_;
    my $options = $self->{options};

    return(undef) if ($options->{blind_cache});

    # make sure it still exists in the filesystem 
    (-r $filepath) or Carp::confess("HTML::Template : template file $filepath does not exist or is unreadable.");

    # get the modification time
    return (stat(_))[9];
}