diff --git a/src/UnrealPackage.cs b/src/UnrealPackage.cs
index a55e504..789978e 100644
--- a/src/UnrealPackage.cs
+++ b/src/UnrealPackage.cs
@@ -2244,7 +2244,7 @@ public void RegisterClass(string className, Type classObject)
         [PublicAPI]
         public void AddClassType(string className, Type classObject)
         {
-            _ClassTypes.Add(className.ToLower(), classObject);
+            _ClassTypes[className.ToLower()] = classObject;
         }
 
         [PublicAPI]