This work presents a method for solving the crystal structure of an organic thin-film prepared on an isotropic surface. Combining specular X-ray diffraction and grazing incidence X-ray diffraction, a full structure solution is exemplarily derived for crystals of the molecule ternaphthalene (NNN). The data are analysed following a classic approach, first, by indexing the Bragg peak pattern and, second, by solving the structure using the experimentally observed intensities. Direct space methods with a rigid-body refinement are applied. The result shows that the NNN crystallizes in a layered herringbone structure. The calculated peak intensities based on this structure are in excellent agreement with the experimentally observed intensities. Overall, following this approach, the crystal structure of the molecule NNN grown in a preferred orientation within thin-films could be unambigously solved providing a general pathway for future thin-film structure solutions.