I argue that the well-known islandhood of adjunct prepositional phrases does not substantially derive from their adjuncthood. Instead, islandhood of these domains derives from various factors that are orthogonal to the argument/adjunct distinction, including PP-internal structure, lexical properties of prepositions, and semantico-pragmatic construal. To show this, I demonstrate that PP-islandhood cross-cuts the argument/adjunct distinction. In particular, (i) PPs with NP complements are generally not islands, (ii) PPs with tensed clausal complements are generally (strong) islands, and (iii) PPs with gerundive complements are generally (weak) islands. These generalizations hold whether or not the relevant PP has a prototypical adjunct function.