Comparison of our stellar tracks computed at solar metallicity with the observed sample of Galactic massive stars collected by Castro et al. (2014). The observations are plotted as a density map in a logarithmic grayscale. We overplot contours of the theoretical distribution of stars obtained from our reference model at Z =  Z_⊙ in color (also in a logarithmic scaling). The lack of observed stars in the parameter range of 3.7 ≲ log(T_eff/K)≲3.9 and 3.5 ≲ log(ℒ/ℒ_⊙) ≲ 4.0 is a tentative piece of evidence that solar metallicity massive stars (mass range of about 16–40 M_⊙) expand until the red giant branch during the HG phase.