Recent studies on the history of composition of the Book of Isaiah generally recognise the secondary character of Isa 10:16-19 in relation to the prophecy against Assyria. It is generally presupposed that these verses elaborate on the famous anti-Assyrian pericope, Isa 10:5-15. Verses 16-19 are most often dated to the seventh century when the book of Isaiah was subject to a major re-edition, the so-called Assyrian redaction, or - more rarely - to the exilic period when the entire book underwent another process of re-reading. Deriving vv. 16-19 from either the late Neo-Assyrian or the Babylonian era involves, however, several difficulties and needs to be reconsidered. While accepting the secondary character of Isa 10:16-19 on its current location, this study proposes a different interpretation and date for this text and assigns it a basically different role in the compositional process of the prophecies in its context than it has so far been proposed.