The bright end of the rest-frame UV luminosity function (UVLF) of high-redshift galaxies is modified by gravitational lensing around foreground structures. This effect is known as magnification bias. In this talk, I will present how the finite size of bright high-redshift galaxies together with lens ellipticity significantly suppresses magnification bias, producing an observed bright end that declines more sharply than the power-law resulting from the assumption of point sources. By assuming a luminosity-size relation for the source population and comparing it with the observed z = 6 galaxy luminosity function from Harikane et al. (2022), I will show that the UVLF can be used to set mild constraints on the galaxies' intrinsic size, favouring smaller galaxies compared to the fiducial luminosity-size relation, and how future wide surveys using Euclid and Roman Space Telescope will place stronger constraints.