diff --git a/components/Icon.js b/components/Icon.js
index a773b9cc..88731cf2 100644
--- a/components/Icon.js
+++ b/components/Icon.js
@@ -10,8 +10,8 @@ const documentLoadedStyleSheets = new Set();
 
 // https://html.spec.whatwg.org/multipage/embedded-content.html#htmlimageelement
 
-/** @implements {Omit<HTMLImageElement,DeprecatedHTMLImageElementProperties>} */
-export default class Icon extends CustomElement
+/** -implements {Omit<HTMLImageElement,DeprecatedHTMLImageElementProperties>} */
+export default CustomElement
   .extend()
   .mixin(ThemableMixin)
   .define({
@@ -204,21 +204,21 @@ export default class Icon extends CustomElement
         documentLoadedStyleSheets.add(href);
       },
     },
-  }) {
-  /**
-   * @param {number} [width]
-   * @param {number} [height]
-   */
-  constructor(width, height) {
-    super();
-
-    if (width != null) {
-      this.width = width;
-    }
-    if (height != null) {
-      this.height = height;
+  })
+  .extend((BaseClass) => class extends BaseClass {
+    /**
+     * @param {number} [width]
+     * @param {number} [height]
+     */
+    constructor(width, height) {
+      super();
+
+      if (width != null) {
+        this.width = width;
+      }
+      if (height != null) {
+        this.height = height;
+      }
     }
-  }
-}
-
-Icon.autoRegister('mdw-icon');
+  })
+  .autoRegister('mdw-icon');
diff --git a/components/ListOption.js b/components/ListOption.js
index 2415e01c..5566eb8f 100644
--- a/components/ListOption.js
+++ b/components/ListOption.js
@@ -4,7 +4,7 @@ import ListItem from './ListItem.js';
 
 // https://html.spec.whatwg.org/multipage/form-elements.html#htmloptionelement
 
-export default class ListOption extends ListItem
+export default ListItem
   .extend()
   .setStatic({
     formAssociated: true,
@@ -146,35 +146,35 @@ export default class ListOption extends ListItem
       background-color: rgb(var(--mdw-bg));
       color: rgb(var(--mdw-ink));
     }
-  ` {
-  static { this.autoRegister('mdw-list-option'); }
-
-  /**
-   * @param {string} [text]
-   * @param {string} [value]
-   * @param {boolean} [defaultSelected]
-   * @param {boolean} [selected]
-   */
-  constructor(text, value, defaultSelected, selected) {
-    super();
-    if (text !== undefined) {
-      this.text = text;
-    }
-    if (value !== undefined) {
-      this._value = value;
-    }
-    if (defaultSelected !== undefined) {
-      this.defaultSelected = defaultSelected;
+  `
+  .extend((BaseClass) => class extends BaseClass {
+    /**
+     * @param {string} [text]
+     * @param {string} [value]
+     * @param {boolean} [defaultSelected]
+     * @param {boolean} [selected]
+     */
+    constructor(text, value, defaultSelected, selected) {
+      super();
+      if (text !== undefined) {
+        this.text = text;
+      }
+      if (value !== undefined) {
+        this._value = value;
+      }
+      if (defaultSelected !== undefined) {
+        this.defaultSelected = defaultSelected;
+      }
+      if (selected !== undefined) {
+        this._selected = selected;
+      }
     }
-    if (selected !== undefined) {
-      this._selected = selected;
-    }
-  }
 
-  connectedCallback() {
-    super.connectedCallback();
-    if (!this.hasAttribute('tabindex')) {
-      this.tabIndex = 0;
+    connectedCallback() {
+      super.connectedCallback();
+      if (!this.hasAttribute('tabindex')) {
+        this.tabIndex = 0;
+      }
     }
-  }
-}
+  })
+  .autoRegister('mdw-list-option');
diff --git a/components/Listbox.js b/components/Listbox.js
index e5747070..340775da 100644
--- a/components/Listbox.js
+++ b/components/Listbox.js
@@ -6,8 +6,7 @@ import StateMixin from '../mixins/StateMixin.js';
 import List from './List.js';
 import ListOption from './ListOption.js';
 
-/** @implements {HTMLSelectElement} */
-// @ts-expect-error Can't implement index signatures (use `item()`)
+/** -implements {HTMLSelectElement} */
 export default List
   .extend()
   .mixin(StateMixin)
diff --git a/components/MenuItem.js b/components/MenuItem.js
index 3583e1fc..65e28a4c 100644
--- a/components/MenuItem.js
+++ b/components/MenuItem.js
@@ -5,7 +5,7 @@ import FormAssociatedMixin from '../mixins/FormAssociatedMixin.js';
 import './Icon.js';
 import ListOption from './ListOption.js';
 
-export default class MenuItem extends ListOption
+export default ListOption
   .extend()
   .mixin(FormAssociatedMixin)
   .set({
@@ -261,5 +261,4 @@ export default class MenuItem extends ListOption
       color: inherit;
     }
   `
-  .autoRegister('mdw-menu-item')
-  .tsClassFix() {}
+  .autoRegister('mdw-menu-item');
diff --git a/components/NavItem.js b/components/NavItem.js
index f5cd0006..6f646814 100644
--- a/components/NavItem.js
+++ b/components/NavItem.js
@@ -11,7 +11,7 @@ import ThemableMixin from '../mixins/ThemableMixin.js';
 
 /** @typedef {'charset'|'coords'|'name'|'shape'} DeprecatedHTMLAnchorElementProperties */
 
-export default class NavItem extends CustomElement
+export default CustomElement
   .extend()
   .mixin(ThemableMixin)
   .mixin(StateMixin)
@@ -269,10 +269,11 @@ export default class NavItem extends CustomElement
       },
     },
   })
-  .autoRegister('mdw-nav-item')
-  .tsClassFix() {
-  addRipple(...args) {
-    if (!this.active) return null;
-    return super.addRipple(...args);
-  }
-}
+  .extend((Base) => class NavItem extends Base {
+    /** @type {InstanceType<ReturnType<RippleMixin>>['addRipple']} */
+    addRipple(...args) {
+      if (!this.active) return null;
+      return super.addRipple(...args);
+    }
+  })
+  .autoRegister('mdw-nav-item');
diff --git a/core/CustomElement.js b/core/CustomElement.js
index f2f0f4f5..971959b4 100644
--- a/core/CustomElement.js
+++ b/core/CustomElement.js
@@ -216,21 +216,11 @@ export default class CustomElement extends ICustomElement {
   /**
    * Extends base class into a new class.
    * Use to avoid mutating base class.
-   * TODO: Add constructor arguments typing
    * @type {typeof ICustomElement.extend}
    */
-  static extend() {
+  static extend(customExtender) {
     // @ts-expect-error Can't cast T
-    return class extends this {};
-  }
-
-  /**
-   * Fix for Typescript not parsing constructor params
-   * @type {typeof ICustomElement.tsClassFix}
-   */
-  static tsClassFix() {
-    // @ts-expect-error Can't cast T
-    return this;
+    return customExtender ? customExtender(this) : class extends this {};
   }
 
   /**
diff --git a/core/ICustomElement.d.ts b/core/ICustomElement.d.ts
index e805ba1f..9f4a248f 100644
--- a/core/ICustomElement.d.ts
+++ b/core/ICustomElement.d.ts
@@ -101,9 +101,10 @@ export declare const ICustomElement: {
 
   schema: Record<string, unknown>;
 
-  extend<T extends typeof ICustomElement>(this: T): T;
-
-  tsClassFix<T extends typeof ICustomElement>(this:T): T & (new (...args:any[]) => InstanceType<T>)
+  extend<T1 extends typeof ICustomElement, T2 extends T1>(
+    this: T1,
+    customExtender?: (Base:T1) => T2
+    ): T2;
 
   html<T extends typeof ICustomElement>(
     this: T,