Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
2. perpĕtŭo, āvi, ātum (old perf. subj. perpetuassint, Enn. Ann. 322), 1, v. a. [perpetuus], to cause a thing to continue uninterruptedly, to proceed with continually, to make perpetual, perpetuate (rare but class.): libertatem ut perpetuassint, Enn. ap. Non. 150, 30 (Ann. v. 322 Vahl.): amator qui perpetuat data, Plaut. Ps. 1, 3, 72: ut si cui sit infinitus spiritus datus, tamen eum perpetuare verba nolimus, Cic. de Or. 3, 46, 181: judicum potestatem perpetuandam … putavit, id. Sull. 22, 64: di te perpetuent, may the gods preserve you! a form of salutation addressed to the emperors, Lampr. Alex. Sev. 6.