We give a necessary and sufficient condition for the existence of a positive principal eigenvalue for a periodic-parabolic problem with indefinite weight function. The condition was originally established by Beltramo and Hess [extit{frenchspacing Comm. Part. https://www.bekindtopets.com/flash-grab-DuramaxTuner-DT8170010101080-Switch-on-the-Fly-Tune-incl-EFI-Live-Spade-cDuramax-LWN-flash-save/