Sorted set a Queue

Question

I needed a data structure offering both poll returning the smallest element and fast contains. A PriorityQueue has slow contains, so I adapted a SortedSet as a queue. I wonder, if I did it right and if using an iterator would be better.

I'm not sure, if I'm bending the semantics of offer too far.

Thanks to Guava and Lombok, my code is very short. Nonetheless, my previous version had a bug, so reviewing it may be a good idea.

@RequiredArgsConstructor
public final class SortedSetAsQueue<E> extends ForwardingSortedSet<E>
implements Queue<E> {
    @Override public boolean offer(E e) {
        return add(e);
    }

    @Override public E remove() {
        final E result = element();
        delegate.remove(result);
        return result;
    }

    @Override @Nullable public E poll() {
        return isEmpty() ? null : remove();
    }

    @Override public E element() {
        return delegate.first();
    }

    @Override @Nullable public E peek() {
        return isEmpty() ? null : element();
    }

    // using lombok.accessors.fluent=true, so no "get" prefix    
    @Getter(value=AccessLevel.PROTECTED)
    private final SortedSet<E> delegate;
}