The modified null field approach to elastic P- and SV-wave scattering (in plane strain) from a partially debonded fiber has been developed. The debonded region on the fiber surface is subjected to traction free boundary conditions, whereas the fiber is assumed to be in welded contact with the host medium elsewhere. Additional null field equations for an elliptical extension of the actual surface of the scatterer are introduced which require additional expansions for the field in the region between the extended mathematical boundary and the actual boundary of the scatterer. The numerical accuracy of the modified null field method has been tested for the case of a perfectly bonded fiber for P- and SV-wave incidence. Scattering cross-section plots are presented for different degrees of debonding.