Can't get path-dependent types to work in scala enumerations

I'm trying to spin my head around the path-dependent types in Scala's enums while making a Reads/Writes for Play2. Here is the code I have so far, it works, but with an asInstanceOf:

implicit def enumerationReads[T <: Enumeration](implicit t: T): Reads[t.Value] = {
    val validationError = ValidationError("error.expected.enum.name", t.values.mkString(", "))
    Reads.of[String].filter(validationError)(s ⇒ t.values.exists(v ⇒ v.toString == s)).map(t.withName(_))
  }

implicit def enumerationValueSetReads[T <: Enumeration](implicit t: T): Reads[t.ValueSet] =
    Reads.seq(enumerationReads[T]).map(seq ⇒ t.ValueSet(seq.asInstanceOf[Seq[t.Value]]: _*))

What can I do to get rid of the asInstanceOf on the last line? I tried typing the enumerationReads as enumerationReads[t.Value], but that doesn't work, the compiler complains in the argument of t.ValueSet that Seq[t.Value] cannot be cast to Seq[t.Value]. Yes, that didn't make sense to me too, until I started to realize these different t's might actually be different, since they are used in a closure.

So, what to do to make my code super-duper asInstanceOf free?