Add "uniqueness" constraint to Decorator Pattern in Java

I am trying to make some pizza with the Decorator Pattern (bear with me):

Suppose I have the following:

interface Pizza {
  public String makePizza();
}
class PlainPizza implements Pizza {
  @Override
  public String makePizza() {
    return "Base Pizza";
  }
}

And then I have a general decorator:

abstract class PizzaDecorator implements Pizza {

  protected Pizza specialPizza;

  public PizzaDecorator(Pizza specialPizza) {
    this.specialPizza = specialPizza;
  }

  public String makePizza() {
    return specialPizza.makePizza();
  }
}

And two implementations of the decorator:

class SausageDecorator extends PizzaDecorator {

  public SausageDecorator(Pizza specialPizza) {
    super(specialPizza);
  }

  public String makePizza() {
    return specialPizza.makePizza() + addSausage();
  }

  private String addSausage() {
    return " + sausage";
  }
}
class OliveDecorator extends PizzaDecorator {

  public OliveDecorator(Pizza specialPizza) {
    super(specialPizza);
  }

  public String makePizza() {
    return specialPizza.makePizza() + addOlives();
  }

  private String addOlives() {
    return " + olives";
  }
}

The problem is that I am able to have duplicate decorators. How can I change the structure of this code to add a "uniqueness" constraint - that is, each Decorator can appear as most once?

class PizzaMaker
    {
        public static void main (String[] args)
        {
            Pizza pizza = new SausageDecorator(new SausageDecorator(new OliveDecorator(new PlainPizza())));
            System.out.println(pizza.makePizza());
        }
    }

Output: Base Pizza + olives + sausage + sausage