Hi @FrankErrickson, thanks for pointing this out. It looks like a Mimi bug, since you should be able to set a parameter as a Distribution type, but we hadn’t thought of that use case so we try to call copy and there is no copy method for Distribution (which is immutable so it doesn’t need one), as the error message shows. I can add a bug fix to this next week, if it’s time sensitive I can also give you a work around in the meantime!