PHPUnit and stubbing Type Hinted Interface/Object?

I have just tried to implement a stub object for a unit test in PHP using PHPUnit.

Normally no problem there.

This time, the object I am stubbing is passed into the constructor of my tested object, but the constructor uses type hinting to an interface.

Everything I try causes an error similar to this one:

ErrorException: Catchable Fatal Error: Argument 1 passed to xxx\xxx\xx::__construct() must be an instance of xxx\xxx\DataRepositoryInterface, instance of Mock_DataRepositoryInterface_9f459e93 given, called in D:\_projects\xxx.php on line 22 and defined in D:\_projects\yyy.php line 12

If anyone has any suggestions about this, I would love to hear them...