The treatment of Proto-Iranian *θw (PIE *t) is one of the isoglosses distinguishing Middle Persian from Parthian and thus important for Western Iranian dialectology. The re-discussion of the Parthian development of this consonant cluster by Nicholas Sims-Williams presents a welcome opportunity for some notes on the matter. I will argue that there is some additional evidence in favour of his suggestion that the Parthian result is not -f- as previously assumed, but a consonant cluster. I will also suggest a modification of the steps that the development takes. The Middle Persian development of *θw as well as some related issues of historical phonology and Pth. orthography and Western Ir. are likewise discussed.