diff --git a/ArcFormats/Silky/ArcAi6Win.cs b/ArcFormats/Silky/ArcAi6Win.cs
index 19c1da38..95f25de0 100644
--- a/ArcFormats/Silky/ArcAi6Win.cs
+++ b/ArcFormats/Silky/ArcAi6Win.cs
@@ -23,6 +23,7 @@
 // IN THE SOFTWARE.
 //
 
+using System;
 using System.Collections.Generic;
 using System.ComponentModel.Composition;
 using System.IO;