JVMS 4.b reads under linking exceptions for WithField:

The field must be final, it must be declared in the current value class, and the
instruction must occur in a method of the current value class. Otherwise,
an IllegalAccessError is thrown.

According to John Rose, this is overly restrictive: "the intention has always been that withfield is a private op. That means nestmates. It’s a VM bug and maybe a spec bug also if withfield works only on the same class. Please, align with the rest of the nestmates work ASAP." and

" The spec. saying “same class” doesn’t know it’s now doing something unusual; private members always used to say “same class” but now the spec. has evolved to talk about nests."