We use the first 100 deg2 of overlap between the Kilo-Degree Survey and the Galaxy And Mass Assembly survey to determine the average galaxy halo mass of ∼10 000 spectroscopically confirmed satellite galaxies in massive (M > 1013 h −1 M⊙) galaxy groups. Separating the sample as a function of projected distance to the group centre, we jointly model the satellites and their host groups with Navarro–Frenk–White density profiles, fully accounting for the data covariance. The probed satellite galaxies in these groups have total masses log 〈M sub/(h −1 M⊙)〉 ≈ 11.7–12.2 consistent across group-centric distance within the errorbars. Given their typical stellar masses, log 〈M ⋆, sat/(h −2 M⊙)〉 ∼ 10.5, such total masses imply stellar mass fractions of 〈M ⋆, sat〉/〈M sub〉 ≈ 0.04 h −1. The average subhalo hosting these satellite galaxies has a mass M sub ∼ 0.015M host independent of host halo mass, in broad agreement with the expectations of structure formation in a Λ cold dark matter universe.