Drush enable module broken

The function to enable a module is broken. I get the following error trying to enable a module:

	

    [drupal] (8.x) $ drush en simpletest
    The following extensions will be enabled: simpletest
    Do you really want to continue? (y/n): y
    PHP Fatal error:  Call to undefined function module_enable() in /home/herjan/Apps/drush/commands/core/drupal/environment.inc on line 148
     
    Fatal error: Call to undefined function module_enable() in /home/herjan/Apps/drush/commands/core/drupal/environment.inc on line 148
    Drush command terminated abnormally due to an unrecoverable error.                                                                                                                         [error]
    Error: Call to undefined function module_enable() in /home/herjan/Apps/drush/commands/core/drupal/environment.inc, line 148