QPointer does not work with virtual inherited QObject

Below example fails at compilation "cannot convert from 'QObject *' to 'C *' but it would be nice to make it work

#include <QObject>
#include <QPointer>

class A : virtual public QObject {
};

class B : virtual public QObject {
};

class C : public A, B {
};

QPointer<C> ptr;
C* foo = ptr;