protected function getCurrencyFromIsoCode($isoCode)
    {
        $this->prepareCurrencies();

        $isoCode = strtolower($isoCode);

        if (!array_key_exists($isoCode, self::$currencies)) {
            throw new UnknownCurrencyException('Currency with '.$isoCode.' iso code does not exist!');
        }

        return self::$currencies[$isoCode];
    }