In a June decision, the Supreme Court in Minerva Surgical v. Hologic, 141 S. Ct. 2298 (2021), breathed new life into the doctrine of assignor estoppel, a centuries-old doctrine based in fundamental fairness principles, that limited an inventor's or an assignor's ability to invalidate a patent it once owned and then transferred for value. But, while the Supreme Court rejuvenated the aging doctrine, it also limited the scope of its application, permitting assignors in certain situations to challenge the validity of the assigned patent in situations where fairness principles should allow.