self::

Hi,
My scripts quit without any error message or any other sign of error as soon as I try to reference a constant defined in the given class with self:: opreator.

class TestController extends Zend_Controller_Action
{
    const constant = 'constant value';

    public function indexAction()
    {
      echo self::constant;
    }
}

Static constants are often referenced this way in ZF, so this holds me back from using such modules as DB or Filters.

I guess my problem is not strictly ZF related, but it has only surfaced in connection with this framework.

Does anyone have any idea on what could cause this problem?
I am using PHP 5.0.5 with Apache 2.x on a debian sarge machine. Is there any extension, that needs to be installed with PHP to get this working?

Thanx in advance

Tibor