protected function _setLineNumber($lineNumber)
    {
        if ($lineNumber !== null) {
            try {
                $lineNumber = $this->_normalizeInt($lineNumber);
            } catch (RootException $e) {
                throw $this->_createInvalidArgumentException($this->__('Invalid line number'), null, $e, $lineNumber);
            }

            if ($lineNumber < 1) {
                throw $this->_createInvalidArgumentException($this->__('Line number must be positive'), null, null, $lineNumber);
            }
        }

        $this->lineNumber = $lineNumber;
    }