In the REPL example,

const nonCallable = { call() {}, bind() {}, apply() {} }

@nonCallable
class C {
  @nonCallable field;
  @nonCallable method() {}
}

we should have asserted the decorator is callable before we invoke the call method, as is required by the spec 7.3.13 Call. We have similar guards for initializers and the decorated class, but somehow we missed the decorators.