InstanceComponentAdapter extends AbstractComponentAdapter, which checks in its constructor for the concreteness of the component class. I have a case where this concreteness check fails (still clearly does not get why...), and i was wondering why this test was useful at all for the InstanceComponentAdapter... I do not know if the test should be removed, but i will try anyway to describe my case hereafter (test case attached): public interface Descriptor { ... public static class DescriptorData { ... } } I register into pico an instance of type Descriptor$DescriptorData[] and this fails... It work of course ok if i comment the call to checkConcrete in AbstractComponentAdapter constructor...