Номер последнего видимого элемента RecyclerView = -1

Подскажите, пожалуйста, почему findLastVisibleItemPosition() возвращает -1

PhotoGalleryFragment.java

public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_photo_gallery, container, false);
        mPhotoRecyclerView = (RecyclerView) v.findViewById(R.id.photo_recycler_view);
        mPhotoRecyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 3));
        ...
        setupAdapter();
        return v;
}
private void setupAdapter() {
        if (isAdded()) {
            if (mPhotoRecyclerView.getAdapter() == null ) {
                mPhotoRecyclerView.setAdapter(new PhotoAdapter(mItems));
                mLastVisibleItemPosition = ((GridLayoutManager)mPhotoRecyclerView
                        .getLayoutManager()).findLastVisibleItemPosition();
                Log.i(TAG, "Последний видимый элемент: " + String.valueOf(mLastVisibleItemPosition));
            } else {
                mPhotoRecyclerView.getAdapter().notifyDataSetChanged();
            }
        }
}