protected function fixHeaders()
    {
        if (count($this->immediateChildren)) {
            $this->setHeaderParameter('Content-Type', 'boundary',
                $this->getBoundary()
                );
            $this->headers->remove('Content-Transfer-Encoding');
        } else {
            $this->setHeaderParameter('Content-Type', 'boundary', null);
            $this->setEncoding($this->encoder->getName());
        }
    }