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.jmannino.com/flash-pick-Navy-Blue-Achkan-Set-With-Mirror-And-Cut-Dana-Embroidery-mega-choice/