PHP override child class property with a property implementing child interface of parent property

I'm having

interface exp_interface
{
}

interface exp_child extends exp_interface
{
}

abstract class A {
protected exp_interface prop;
}

And I want to have a A child like this:

class A_child {
protected exp_child prop;
}

PHP is not allowing this, although technically, A_child.prop DOES implement exp_interface, since exp_child extends exp_interface.

Is there anyway to achieve this desired outcome ?