Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ob-stŭpĕ-făcĭo, fēci, factum, 3, v. a.; in pass. obstŭpĕfīo, factus, fieri, to astonish, amaze, astound, stupefy; to render senseless, deprive of feeling, benumb (class.): eum timidum obstupefecit pudor, Ter. Phorm. 2, 1, 54: ipso miraculo audaciae obstupefecit hostes, Liv. 2, 10: nisi metus maerorem obstupefaceret, id. 25, 38; cf. Tac. H. 4, 72.
Pass.: obstupefactis hominibus, Cic. Deiot. 12, 34: obstupefacti hostes, Tac. Agr. 18: obstupefactis nervis, Val. Max. 3, 8, ext. 6.