diff --git a/dECS/Core.h b/dECS/Core.h
index bdfe6af9..1b3127a8 100644
--- a/dECS/Core.h
+++ b/dECS/Core.h
@@ -13,8 +13,8 @@ namespace dECS {
     // concept IsComponent = std::derived_from<C, Component>;
 
     struct WorldData;
-    struct World;
-    struct Entity;
+    class World;
+    class Entity;
     struct IStorage;
 
     template <typename C>