Error trying to use query builder (version 4.04)

I'm receiving this error:

• Argument 1 passed to App\Models\PostModel::App\Models\{closure}() must be an instance of App\Models\BaseBuilder
  

When I try to use the "orWhereIn" method of the query builder like so:

$results = $this->select('id, body, timestamp, user_id')
                       ->where('user_id', $userID)
                       ->orWhereIn('id', function(BaseBuilder $subq) {
                               return $subq->select('followed_id')
                                                  ->from('followers')
                                                  ->where('follower_id', $userID);
                               })
                        ->orderBy('timestamp', 'DESC')
                        ->findAll();


The "$this" above is in context with the model I am in, so I am using the built-in query builder instance of the model. I have the initial table set up by a "protected $table" declaration (thus no from clause under the first select).

Not sure how to fix it - can anyone help?