diff --git a/packages/GameCult.Thing.Contract/Command.cs b/packages/GameCult.Thing.Contract/Command.cs
index 9cf3a91..8b217a5 100644
--- a/packages/GameCult.Thing.Contract/Command.cs
+++ b/packages/GameCult.Thing.Contract/Command.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using GameCult.Caching;
 using MessagePack;