@Override
  @J2ktIncompatible // serialization
  Object writeReplace() {
    return new EnumSerializedForm<>(delegate);
  }

  @J2ktIncompatible // serialization
  private void readObject(ObjectInputStream stream) throws InvalidObjectException {
    throw new InvalidObjectException("Use EnumSerializedForm");
  }

  /*
   * This class is used to serialize ImmutableEnumMap instances.
   */

  /*
   * This class is used to serialize ImmutableEnumSet instances.
   */
  @J2ktIncompatible // serialization
  private static final class EnumSerializedForm<E extends Enum<E>> implements Serializable {
    final EnumSet<E> delegate;

    EnumSerializedForm(EnumSet<E> delegate) {
      this.delegate = delegate;
    }

    Object readResolve() {
      // EJ2 #76: Write readObject() methods defensively.