diff --git a/.changeset/smooth-apricots-laugh.md b/.changeset/smooth-apricots-laugh.md
new file mode 100644
index 000000000..579c137ff
--- /dev/null
+++ b/.changeset/smooth-apricots-laugh.md
@@ -0,0 +1,5 @@
+---
+'@lion/form-core': patch
+---
+
+Remove usage of Public Class Fields to not break builds
diff --git a/packages/babel-plugin-extend-docs/demo/src/MyCounter.js b/packages/babel-plugin-extend-docs/demo/src/MyCounter.js
index d2f57c8be..b31fe8278 100644
--- a/packages/babel-plugin-extend-docs/demo/src/MyCounter.js
+++ b/packages/babel-plugin-extend-docs/demo/src/MyCounter.js
@@ -1,9 +1,11 @@
 import { LitElement, html, css } from 'lit-element';
 
 export class MyCounter extends LitElement {
-  static properties = {
-    count: { type: Number },
-  };
+  static get properties() {
+    return {
+      count: { type: Number },
+    };
+  }
 
   static styles = css`
     :host {
diff --git a/packages/form-core/src/registration/FormRegisteringMixin.js b/packages/form-core/src/registration/FormRegisteringMixin.js
index 66b580476..6060275b2 100644
--- a/packages/form-core/src/registration/FormRegisteringMixin.js
+++ b/packages/form-core/src/registration/FormRegisteringMixin.js
@@ -16,8 +16,11 @@ import { dedupeMixin } from '@lion/core';
  */
 const FormRegisteringMixinImplementation = superclass =>
   class extends superclass {
-    /** @type {FormRegistrarHost | undefined} */
-    __parentFormGroup;
+    constructor() {
+      super();
+      /** @type {FormRegistrarHost | undefined} */
+      this.__parentFormGroup = undefined;
+    }
 
     connectedCallback() {
       // @ts-expect-error check it anyway, because could be lit-element extension