Orbital period derivative of XB 1916-053 in units of 10^-11 s s^-1 versus the thermal bloating factor f of the companion star. The brown and purple curves are obtained using a NS mass of 2.1 and 2.2 M_⊙. The red and green lines indicate the best-fit value and the values at 68% confidence level of the orbital period derivative obtained from the LQS ephemeris. The purple curve is compatible at 1σ with the measured orbital period derivative for f ≃ 1.5.