Book The Rest: Listing 28 and 30 contain the following line: ```c++ shared_ptr<hittable> light_shape = make_shared<xz_rect>(213, 343, 227, 332, 554, 0); ``` `xz_rect` requires a pointer as its last argument. The source code contains the correct, and probably intended, version: ```c++ shared_ptr<hittable> light_shape = make_shared<xz_rect>(213, 343, 227, 332, 554, make_shared<material>()); ```