Abstract. For ordinary modular forms, there are two constructions of a padic L-function attached to the non-unit root of the Hecke polynomial, which are conjectured but not known to coincide. We prove this conjecture for modular forms of CM type, by calculating the the critical-slope L-function arising from Kato's Euler system and comparing this with results of Bellaïche on the critical-slope L-function defined using overconvergent modular symbols.