Properties of the Kepler-91 system from a comparative perspective. We plot the semi-major axis of all confirmed planets (grey circles) against the stellar radius (left) and the surface gravity (right). In the left panel, the red point marks the position of Kepler-91 and the solid line is the location of the stellar radius (1:1 line), showing that, among giant stars, this is the closest planet to the stellar surface. In the right panel, we can check that Kepler-91 lies below the solid line marking the empirical limit suggested by Nowak et al. (2013). Together with the intriguing case of HIP 13044, Kepler-91 is the only planet that goes through this line.