Isolate.Swap.CallsOn issue

In tested assembly:
class A{
protected internal int Do(int i);
}


Assembly with tests is marked with InetnalsVisible for tested assembly

class Fake{
public int Do(int i);
}


when I try to do the following i get exception
Isolate.Swap.CallsOn(AInstance).WithCallsTo(FakeInstance);

but if I change A class method to be public, it works fine

exception has message "no matching methods found"

I tried to make Fake method protected internal, no luck...