diff --git a/src/utils/class.js b/src/utils/class.js
index 290f36d1..6b062d90 100644
--- a/src/utils/class.js
+++ b/src/utils/class.js
@@ -46,7 +46,7 @@ export function extendClassStaticProps(childClass, parentClass, excludedProps =
 export function extendThis(child, childClass, parentClass, excludedProps = [], ...args) {
     let props;
     let obj = new parentClass.prototype.constructor(...args);
-    const exclude = ["constructor", ...Object.getOwnPropertyNames(childClass)];
+    const exclude = ["constructor", ...Object.getOwnPropertyNames(childClass.prototype)];
     const seen = []; // remember most recent occurrence of prop name (like inheritance)
     while (obj.__proto__) {
         props = Object.getOwnPropertyNames(obj.__proto__);