Thanks @karelpeeters. The message seems to apply mainly to type arguments (i.e., outside the generic class at the use site rather than inside the class declaration). I traced the error message in the Kotlin compiler code back to April 2012... so I'm thinking either Kotlin tried to support generic property access at one point early in its history (although I'm not sure how that would conceptually work), or the message was just written incorrectly. Maybe I can ask one of the JetBrains guys at the next KotlinConf. 🙂