diff --git a/tools/index-tools/src/org/jetbrains/index/id/IdIndexGenerator.kt b/tools/index-tools/src/org/jetbrains/index/id/IdIndexGenerator.kt
index 8e91bd88c6b9..32082c82af3b 100644
--- a/tools/index-tools/src/org/jetbrains/index/id/IdIndexGenerator.kt
+++ b/tools/index-tools/src/org/jetbrains/index/id/IdIndexGenerator.kt
@@ -26,7 +26,7 @@ open class IdIndexGenerator(private val idIndexStorageFilePath: String) : IndexG
                              HashCodeDescriptor.instance, IdIndexMapDataExternalizer())
   }
 
-  fun buildIdIndexForRoots(rootFiles: ArrayList<VirtualFile>) {
+  fun buildIdIndexForRoots(rootFiles: List<VirtualFile>) {
     buildIndexForRoots(rootFiles)
   }
 }