diff --git a/library/collection/List.scala b/library/collection/List.scala
index b739aa3bb32c40e1912bfaddc55c7917d97426d1..399ef5b83332196f4d006db16668ad4fd2686fae 100644
--- a/library/collection/List.scala
+++ b/library/collection/List.scala
@@ -16,6 +16,8 @@ sealed abstract class List[T] {
     case Cons(h, t) => 1 + t.size
   }) ensuring (_ >= 0)
 
+  def length = size
+
   def content: Set[T] = this match {
     case Nil() => Set()
     case Cons(h, t) => Set(h) ++ t.content