diff --git a/packages/happy-dom/src/config/NonImplemenetedElementClasses.ts b/packages/happy-dom/src/config/NonImplemenetedElementClasses.ts
index 94b9dc358..6727c9415 100644
--- a/packages/happy-dom/src/config/NonImplemenetedElementClasses.ts
+++ b/packages/happy-dom/src/config/NonImplemenetedElementClasses.ts
@@ -21,7 +21,6 @@ export default [
 	'HTMLDataElement',
 	'HTMLDataListElement',
 	'HTMLDetailsElement',
-	'HTMLDialogElement',
 	'HTMLDirectoryElement',
 	'HTMLFieldSetElement',
 	'HTMLFontElement',
diff --git a/packages/happy-dom/src/nodes/html-dialog-element/HTMLDialogElement.ts b/packages/happy-dom/src/nodes/html-dialog-element/HTMLDialogElement.ts
index 0d69e9d94..130ecc469 100644
--- a/packages/happy-dom/src/nodes/html-dialog-element/HTMLDialogElement.ts
+++ b/packages/happy-dom/src/nodes/html-dialog-element/HTMLDialogElement.ts
@@ -9,12 +9,7 @@ import IHTMLDialogElement from './IHTMLDialogElement';
  * https://developer.mozilla.org/en-US/docs/Web/API/HTMLDialogElement.
  */
 export default class HTMLDialogElement extends HTMLElement implements IHTMLDialogElement {
-	/**
-	 * Returns returnValue.
-	 *
-	 * @returns ReturnValue.
-	 */
-	public returnValue: string;
+	public returnValue = '';
 
 	/**
 	 * Returns open.
@@ -28,12 +23,12 @@ export default class HTMLDialogElement extends HTMLElement implements IHTMLDialo
 	/**
 	 * Closes the dialog.
 	 *
-	 * @param returnValue ReturnValue.
+	 * @param [returnValue] ReturnValue.
 	 */
-	public close(returnValue?: string): void {
+	public close(returnValue = ''): void {
 		this.removeAttributeNS(null, 'open');
 		this.returnValue = returnValue;
-		this.dispatchEvent(new Event('close', { bubbles: false, cancelable: false }));
+		this.dispatchEvent(new Event('close'));
 	}
 
 	/**
diff --git a/packages/happy-dom/src/nodes/html-dialog-element/IHTMLDialogElement.ts b/packages/happy-dom/src/nodes/html-dialog-element/IHTMLDialogElement.ts
index 4fbf8c455..2633a9356 100644
--- a/packages/happy-dom/src/nodes/html-dialog-element/IHTMLDialogElement.ts
+++ b/packages/happy-dom/src/nodes/html-dialog-element/IHTMLDialogElement.ts
@@ -9,7 +9,21 @@ import IHTMLElement from '../html-element/IHTMLElement';
 export default interface IHTMLDialogElement extends IHTMLElement {
 	open: boolean;
 	returnValue: string;
+
+	/**
+	 * Closes the dialog.
+	 *
+	 * @param [returnValue] ReturnValue.
+	 */
 	close(returnValue?: string): void;
+
+	/**
+	 * Shows the modal.
+	 */
 	showModal(): void;
+
+	/**
+	 * Shows the dialog.
+	 */
 	show(): void;
 }
diff --git a/packages/happy-dom/test/nodes/html-dialog-element/HTMLDialogElement.test.ts b/packages/happy-dom/test/nodes/html-dialog-element/HTMLDialogElement.test.ts
index 583008b68..601757b7c 100644
--- a/packages/happy-dom/test/nodes/html-dialog-element/HTMLDialogElement.test.ts
+++ b/packages/happy-dom/test/nodes/html-dialog-element/HTMLDialogElement.test.ts
@@ -1,20 +1,21 @@
-import { Event } from 'src';
-import Document from '../../../src/nodes/document/Document';
-import HTMLDialogElement from '../../../src/nodes/html-dialog-element/HTMLDialogElement';
+import Event from '../../../src/event/Event';
+import IHTMLDialogElement from '../../../src/nodes/html-dialog-element/IHTMLDialogElement';
 import Window from '../../../src/window/Window';
+import IWindow from '../../../src/window/IWindow';
+import IDocument from '../../../src/nodes/document/IDocument';
 
 describe('HTMLDialogElement', () => {
-	let window: Window;
-	let document: Document;
-	let element: HTMLDialogElement;
+	let window: IWindow;
+	let document: IDocument;
+	let element: IHTMLDialogElement;
 
 	beforeEach(() => {
 		window = new Window();
 		document = window.document;
-		element = <HTMLDialogElement>document.createElement('dialog');
+		element = <IHTMLDialogElement>document.createElement('dialog');
 	});
 
-	describe('open', () => {
+	describe('get open()', () => {
 		it('Should be closed by default', () => {
 			expect(element.open).toBe(false);
 		});
@@ -30,23 +31,25 @@ describe('HTMLDialogElement', () => {
 		});
 	});
 
-	describe('returnValue', () => {
-		it('Should be undefined by default', () => {
-			expect(element.returnValue).toBe(undefined);
+	describe('get returnValue()', () => {
+		it('Should be empty string by default', () => {
+			expect(element.returnValue).toBe('');
 		});
 
 		it('Should be set when close has been called with a return value', () => {
 			element.close('foo');
 			expect(element.returnValue).toBe('foo');
 		});
+	});
 
+	describe('set returnValue()', () => {
 		it('Should be possible to set manually', () => {
 			element.returnValue = 'foo';
 			expect(element.returnValue).toBe('foo');
 		});
 	});
 
-	describe('close', () => {
+	describe('close()', () => {
 		it('Should be possible to close an open dialog', () => {
 			element.show();
 			element.close();
@@ -92,7 +95,7 @@ describe('HTMLDialogElement', () => {
 		});
 	});
 
-	describe('showModal', () => {
+	describe('showModal()', () => {
 		it('Should be possible to show a modal dialog', () => {
 			element.showModal();
 			expect(element.open).toBe(true);
@@ -100,7 +103,7 @@ describe('HTMLDialogElement', () => {
 		});
 	});
 
-	describe('show', () => {
+	describe('show()', () => {
 		it('Should be possible to show a dialog', () => {
 			element.show();
 			expect(element.open).toBe(true);