drush colorbox-plugin fails

Running drush colorbox-plugin with Drush 4.5 results in this PHP Fatal error:

PHP Fatal error:  Call to undefined function drush_download_file() in /var/www/drupal/sites/all/modules/colorbox/drush/colorbox.drush.inc on line 111
Drush command terminated abnormally due to an unrecoverable error. [error]
Error: Call to undefined function drush_download_file() in /var/www/drupal/sites/all/modules/colorbox/drush/colorbox.drush.inc, line 111

sites/all/libraries does exist and is successfully being used by other libs.

Manually downloading and unpacking the lib works, as usual.