diff --git a/SkinHide/Utils/RefHelp.cs b/SkinHide/Utils/RefHelp.cs
index 16b6ae4..0644250 100644
--- a/SkinHide/Utils/RefHelp.cs
+++ b/SkinHide/Utils/RefHelp.cs
@@ -262,7 +262,7 @@ namespace SkinHide.Utils
             }
         }
 
-        public class FieldRef<T, F>
+        public class FieldRef<T, F> where T : class
         {
             private AccessTools.FieldRef<T, F> HarmonyFieldRef;