packages/happy-dom/src/nodes/document/Document.ts

@@ -318,8 +318,8 @@ export default class Document extends Node {
 	/**
 	 * Returns a collection of all form elements in a document.
 	 */
-	public get forms(): NodeList<HTMLFormElement> {
-		return this.querySelectorAll('form');
+	public get forms(): HTMLCollection<HTMLFormElement> {
+		return this.getElementsByTagName('form');
 	}
 
 	/**

packages/happy-dom/test/nodes/document/Document.test.ts

@@ -124,6 +124,7 @@ describe('Document', () => {
 
 			const forms = document.forms;
 
+			expect(forms).toBeInstanceOf(HTMLCollection);
 			expect(forms.length).toBe(2);
 			expect(forms[0]).toBe(form1);
 			expect(forms[1]).toBe(form2);