ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(serializedForm));

    ImmutableSet<?> deserialized = (ImmutableSet<?>) in.readObject();
    EnumSet<?> delegate = (EnumSet<?>) in.readObject();

    assertEquals(original, deserialized);
    assertTrue(delegate.remove(SomeEnum.A));
    assertTrue(deserialized.contains(SomeEnum.A));
  }

  @J2ktIncompatible