Previous discussions (Mester, 1990; Poser, 1990) of nickname formation in Japanese with /chan/ have noted three prominent forms: SIMPLE (kumiko -> kumichan), V-LENGTHENED (masahiro -> maachan) and GEMINATED (sachiko -> sacchan). Poser made two claims about these forms: (1) the SIMPLE form is always possible and (2) for a name beginning with (C1) V1 t V2 [+HIGH], the GEMINATED form is preferred. The present investigation reports on an experiment designed to test these claims by getting native judgments on nicknames formed from a wide variety of attested names. Results confirm claim (2) but not claim (1). Beginning with Tsuchida's (2001) account of high-vowel devoicing, I present an Optimality-theoretic (Prince and Smolensky, 1993) account of nickname formation using variable constraint ranking (Antilla, 1997).