diff --git a/idea/src/jet/Library.jet b/idea/src/jet/Library.jet
index 950ea00e93e..960b26ce3fc 100644
--- a/idea/src/jet/Library.jet
+++ b/idea/src/jet/Library.jet
@@ -47,6 +47,9 @@ class String() : Comparable<String> {
 
   fun plus(other : Any?) : String
   fun equals(other : Any?) : Boolean
+
+  fun substring(start: Int): String
+  fun substring(start: Int, end: Int): String
 }
 
 class Range<in T : Comparable<T>> {