Wildcard capture in Java, unable to call a method

I currently have three classes and trying to implement Generic Visitor pattern for putting it into a library shared among all our projects:

public interface Visitable<ReturnType> {

    public ReturnType accept(Visitor<?, ?> v);

}

public interface Visitor<SomeVisitable extends Visitable<?>, ReturnType> {

    public ReturnType visit(SomeVisitable v);

}

public class BaseObject implements Visitable<Void>{
    public Void accept(Visitor<?, ?> v) {
        v.visit(this); //1
                       // The method visit(capture#1-of ?) in the type                                        
                       // Visitor<capture#1-of ?,capture#2-of ?> is not
                       // applicable for the arguments (BaseObject)
    }
}

Why did I get the compile-time error at //1? Honestly I really don't know what I should redisign in that code to make it compile.