diff --git a/library/lang/Map.scala b/library/lang/Map.scala
index 8df83e6e1b678dfe2722515633f914ed93f3f76f..fec77314260b341d861d39e456c7f8e5a7775eb2 100644
--- a/library/lang/Map.scala
+++ b/library/lang/Map.scala
@@ -2,6 +2,7 @@ package leon.lang
 import leon.annotation._
 
 object Map {
+  @library
   def empty[A,B] = Map[A,B]()
 }
 
diff --git a/library/lang/Set.scala b/library/lang/Set.scala
index dcedd1e0b06c865f8f49edab5b13d5f347181844..086b31988ec238f8b692269f73b0c24b8e04417c 100644
--- a/library/lang/Set.scala
+++ b/library/lang/Set.scala
@@ -2,6 +2,7 @@ package leon.lang
 import leon.annotation._
 
 object Set {
+  @library
   def empty[T] = Set[T]()
 }