Influence of the surface morphology on the resultant RBS spectra in channeling configuration is studied. It is shown that the energy distribution of the 'damage peak' critically depends on the extent of the surface roughness. The observed tailoring of the surface damage peak towards low energies in the spectrum of the backscattered particles can be easily misinterpreted as in-depth profile of the concentration of defects. Simple analysis indicates that this effect is of purely geometrical nature. It becomes significant when dimension and spacing of the surface features are within the range from the actual depth resolution up to the sampling depth. Experiments illustrating the above findings were performed on (100)InP sputter-etched with Ar ions at energies of 0.5-4 keV. Correlation between the population of the conical features which develop upon ion milling and the corresponding distortion of the channeling spectrum is demonstrated.