diff --git a/packages/reffuse/src/ReffuseExtension.ts b/packages/reffuse/src/ReffuseExtension.ts
index 0ba7909..f15af1b 100644
--- a/packages/reffuse/src/ReffuseExtension.ts
+++ b/packages/reffuse/src/ReffuseExtension.ts
@@ -2,7 +2,7 @@ import * as ReffuseHelpers from "./ReffuseHelpers.js"
 import type { Merge, StaticType } from "./types.js"
 
 
-export const make = <Ext extends object>(extension: Ext) =>
+export const make = <Ext extends object>(extension: () => Ext) =>
     <
         BaseClass extends ReffuseHelpers.ReffuseHelpersClass<R>,
         R
@@ -13,6 +13,6 @@ export const make = <Ext extends object>(extension: Ext) =>
         StaticType<BaseClass>
     ) => {
         const class_ = class extends self {}
-        class_.prototype = { ...class_.prototype, ...extension } as any
+        Object.assign(class_.prototype, extension())
         return class_ as any
     }