}

      // We can't use .clone() because of GWT.
      byte[] newDecodabet = Arrays.copyOf(decodabet, decodabet.length);
      for (int upper = 'A'; upper <= 'Z'; upper++) {
        int lower = upper | 0x20;
        byte decodeUpper = decodabet[upper];
        byte decodeLower = decodabet[lower];
        if (decodeUpper == -1) {
          newDecodabet[upper] = decodeLower;
        } else {
          checkState(