Добавление двух Set [Any]

Добавление двух Set [Int] работает:

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scala> Set(1,2,3) ++ Set(4,5,6)          
res0: scala.collection.immutable.Set[Int] = Set(4, 5, 6, 1, 2, 3)

Но добавление двух Set [Any] не работает:

scala> Set[Any](1,2,3) ++ Set[Any](4,5,6)
<console>:6: error: ambiguous reference to overloaded definition,
both method ++ in trait Addable of type (xs: scala.collection.TraversableOnce[Any])scala.collection.immutable.Set[Any]
and  method ++ in trait TraversableLike of type [B >: Any,That](that: scala.collection.TraversableOnce[B])(implicit bf: scala.collection.generic.CanBuildFrom[scala.collection.immutable.Set[Any],B,That])That
match argument types (scala.collection.immutable.Set[Any])
   Set[Any](1,2,3) ++ Set[Any](4,5,6)
           ^

Любые предложения по работе эта ошибка?