Constraints on the neutron star mass in EXO 0748−676. Under the assumption that the companion is filling its Roche lobe, the eclipse measurement of the eclipse duration gives a relation between the mass ratio q=M₂/M₁ and the inclination of the orbit (Horne 1985). Furthermore, the mass ratio relates to the rotational velocity v sin i and the radial velocity semi-amplitude K₂. The dashed lines show curves for specific rotational velocities. Finally, the neutron star mass function relates the neutron star mass to the mass ratio and the radial velocity semi-amplitude, giving the solid lines for specific neutron star masses. The horizontal grey area is excluded by our lower limit on the radial velocity semi-amplitude of K_em= 410 ± 5 km s⁻¹, setting K₂ > 405 km s⁻¹, while the diagonal grey area is excluded in order to satisfy that all emission originates between the radial velocity of L1 and the centre of mass of the companion (V_L1 < K_em < K₂). These constraints dictate that the neutron star is heavier than M₁ > 1.27 M_⊙. The hashed area is the mass range of M₁= 2.10 ± 0.28 M_⊙ favoured by the work of Özel (2006).