Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sŭper-fīgo, ĕre, fixus, 3, v. n., to fasten up, fasten thereupon: superfixa capita hostium portantes redierunt, Liv. 42, 60, 2; Treb. Pol. Claud. 3, 5.