The strength functions for the giant dipole resonance in heated ⁹⁰Zr are calculated within the framework of the finite temperature quasiparticle-phonon nuclear model. For the strength functions a Lorentzian factor of width dependent upon state energies and temperature T is adopted. Shape fluctuations are taken into account at the excitation energy corresponding to T=1.5 MeV and I=7.5 h(cross). While the effect of the Landau zero sound damping on the broadening of the dipole strength distribution changes weakly with T, shape fluctuations increase remarkably the width of the giant dipole resonance. They influence profoundly the structural modifications of the dipole strength distribution at finite temperature.