We study the effect of fluctuations in opening angle of bent-core molecules on stability of the nematic phases. The molecules are built out of two Gay-Berne centers each corresponding to one of the molecular arms. Constant-pressure Monte Carlo (MC NPT) simulations are carried out for two versions of the model, with fixed- and fluctuating opening angle, where fluctuations are taken harmonic about the angle of 140 degrees. The phases found on cooling are uniaxial nematic, biaxial nematic and crystalline. On heating the biaxial nematic is superseded by the metastable crystalline phase.