GtkTextView->get_iter_at_location bug or user error?

["Beanz" <gtk-perl beanz uklinux net>]

What I am doing wrong? If I defined a button_press_event callback on 
a GtkTextView like:

  sub clicked {
    my $widget = $_[0];
    my $event = $_[1];
  
    print STDERR "Widget: $widget\nEvent: $event\n";
    my $iter = $widget->get_iter_at_location($event->x, $event->y);
    # blah, blah
    return 0;
  }

$widget and $event are as expected, but I get a usage error:

  Usage: Gtk2::TextView::get_iter_at_location(text_view, iter, x, y) at ...

This is with 0.91. Any help much appreciated.

Regards,
 Beanz.