diff --git a/ObservatoryFramework/Files/Journal/Powerplay/PowerplayVoucher.cs b/ObservatoryFramework/Files/Journal/Powerplay/PowerplayVoucher.cs
index d7a24d5..3c9d4f2 100644
--- a/ObservatoryFramework/Files/Journal/Powerplay/PowerplayVoucher.cs
+++ b/ObservatoryFramework/Files/Journal/Powerplay/PowerplayVoucher.cs
@@ -1,4 +1,6 @@
-namespace Observatory.Framework.Files.Journal
+using System.Collections.Immutable;
+
+namespace Observatory.Framework.Files.Journal
 {
     public class PowerplayVoucher : PowerplayJoin
     {