const qobject_cast for interfaces

[Asperamanca]

I like to use Q_DECLARE_INTERFACE, because it allows me to use qobject_cast for these interfaces (provided the implementation has the Q_INTERFACES makro)

All works well, until I try to cast a const instance.

So this works:
ISomeInterface* pInterface = qobject_cast<ISomeInterface*>(pSomeObject);

And this doesn't:
const ISomeInterface* pInterface = qobject_cast<const ISomeInterface*>(pSomeObject);

Error message is:
'const class ISomeInterface' has no member named 'qt_check_for_QOBJECT_macro'
'const class ISomeInterface' has no member named 'qt_check_for_QOBJECT_macro'

Any ideas?