Deviation of the fitted value of the planet radius and its exact value as a function of the planet-spot overlap. In cases 1 to 3, the transiting planet has a radius of R_p/R_∗ = 0.1, the spot has zero-brightness and a filling factor of 1%, and the limb-darkening coefficients are (u₁,u₂) = (0.29,0.34), (0.38, 0.37), and (0.6, 0.16), respectively. Case 4 is similar to case 1 with the brightness of the stellar spot increased to 50%.