private function ensureCorrectColumnType()
    {
        if (!$this->database->tableExists('tl_metamodel_attribute')) {
            return;
        }

        $attributes = $this
            ->database
            ->prepare(
                'SELECT metamodel.tableName, attribute.colname
                FROM tl_metamodel_attribute AS attribute
                LEFT JOIN tl_metamodel AS metamodel
                ON (metamodel.id=attribute.pid)
                WHERE attribute.type=?'
            )
            ->execute('combinedvalues');

        while ($attributes->next()) {
            $this
                ->database
                ->execute(
                    \sprintf(
                        'ALTER TABLE %1$s CHANGE COLUMN %2$s %2$s %3$s',
                        $attributes->tableName,
                        $attributes->colname,
                        'text NULL'
                    )
                );
        }
    }