Appellant was convicted of failing to register as a sex offender, and on appeal argued that his conviction violated due process and ex post facto principles in that he had no actual notice or knowledge that he was required to register at two addresses, as that provision was not incorporated into section 290 until after his trial. The jury was not instructed that they could not convict absent evidence that the defendant knew about the registration requirement. Therefore, the instructions were erroneous. Since there was no evidence of defendant’s actual knowledge that he knew he was required to register additional addresses, the error was not harmless and reversal was required.