How to declare operator++(int) in an abstract class?

I have an abstract class that is basically meant to serve as an "iterator interface". That is, it is an abstract iterator that a few concrete classes will later implement. To make the abstract class an iterator, I need to overload T operator++(int), where T is the class for which the operator is overloaded.

class AbstractClass {
    virtual AbstractClass operator++(int) = 0; // compile time error
    virtual AbstractClass& operator++() = 0;   // but this is fine
}

However, I cannot write AbstractClass operator++(int) as only pointers and references to an abstract class are permitted as return values.

Is there a way to require the subclasses to overload operator++(int) in plain C++11?