Upper limits on the minimum mass of a possible planetary companion of CoRoT-9b with 99% confidence level as a function of orbital period up to 5 years. Black and shaded areas refer to circular and eccentric orbits of the hypothetical companion; the maximum allowed eccentricity for each period was derived from dynamical stability criteria (see text for more details). The empty region around the orbital period of CoRoT-9b (P = 95.27 d) is dynamically unstable for the minimum planetary masses detectable with our HARPS RV data.