Dynamical stability of the RZ Dra system as a function of the semi-major axis, a, and eccentricity, e of RZ Dra (AB) D for the alternative solution. The nominal best-fit orbit for RZ Dra (AB) D is located in the center of the red box, at a = 26.6 AU and e = 0.62. The 1σ uncertainties on the semi-major axis and eccentricity are shown by a crosshair. Almost all the tested models, particularly those within the ± 1σ uncertainties, are dynamically unstable on remarkably short timescales. A few regions are stable on timescales of around a million years, but these are all located at the extreme edges of the plot, almost ± 3σ away from the nominal best-fit orbit. The black dot is the location of a test orbit as discussed in Sect. 2. This figure is available in color in electronic form.