This is a good example of the high levels of suspicion to which occurrence of "symbol.tpe" aka "symbol.tpe_*" should be subject. This change alters the created type though. clazz.tpe will get the symbol dummies wrapped around whatever type parameters might be associated with it, whereas you are explicitly giving Nil. That change, although seemingly innocuous given that the type arguments are supposed to be replaced, seems unrelated to the basis for this PR, that being the prefix. Is it intentional?