diff --git a/library/lang/Rational.scala b/library/lang/Rational.scala
index 3be89a7632a42b6b17d069435bf15ce00bea8912..e2d6f758873623a8ed7c1ccee8a973b4264dca6e 100644
--- a/library/lang/Rational.scala
+++ b/library/lang/Rational.scala
@@ -4,6 +4,8 @@ package leon.lang
 
 import leon.annotation._
 
+import scala.language.implicitConversions
+
 @library
 case class Rational(numerator: BigInt, denominator: BigInt) {