diff --git a/AutoDiff/Core/AutoDiff/ReadOnlyListWrapper.cs b/AutoDiff/Core/AutoDiff/ReadOnlyListWrapper.cs
index 468b37e..9ac1e9c 100644
--- a/AutoDiff/Core/AutoDiff/ReadOnlyListWrapper.cs
+++ b/AutoDiff/Core/AutoDiff/ReadOnlyListWrapper.cs
@@ -1,4 +1,5 @@
-using System.Collections;
+using System;
+using System.Collections;
 using System.Collections.Generic;
 
 namespace AutoDiff