We have performed time-of-flight neutron powder diffraction experiments on Tb_1-xPr_xCu₂ compounds to study the concentration dependence of the crystal and magnetic structures. The mixed compounds crystallize in the same space group Imma as the pure RCu₂ with R atoms randomly distributed on the 4e sites. The type of magnetic ordering is the same as for the end concentration TbCu₂. A characteristic broadening of the magnetic reflections belonging to the third harmonics of the magnetic structure is observed.