diff --git a/packages/happy-dom/src/xml-serializer/XMLSerializer.ts b/packages/happy-dom/src/xml-serializer/XMLSerializer.ts
index 75d9bea39..b1ffadb10 100644
--- a/packages/happy-dom/src/xml-serializer/XMLSerializer.ts
+++ b/packages/happy-dom/src/xml-serializer/XMLSerializer.ts
@@ -42,7 +42,7 @@ export default class XMLSerializer {
 				}
 
 				if (options?.includeShadowRoots && element.shadowRoot) {
-					innerHTML += `<template shadowroot="${element.shadowRoot.mode}">`;
+					innerHTML += `<template shadowrootmode="${element.shadowRoot.mode}">`;
 
 					for (const node of element.shadowRoot.childNodes) {
 						innerHTML += this.serializeToString(node, options);
diff --git a/packages/happy-dom/test/xml-serializer/XMLSerializer.test.ts b/packages/happy-dom/test/xml-serializer/XMLSerializer.test.ts
index 2475c0653..2f1c263c6 100644
--- a/packages/happy-dom/test/xml-serializer/XMLSerializer.test.ts
+++ b/packages/happy-dom/test/xml-serializer/XMLSerializer.test.ts
@@ -157,7 +157,7 @@ describe('XMLSerializer', () => {
 					<div>
 						<custom-element key1="value1" key2="value2">
 							<span>Slotted content</span>
-							<template shadowroot="open">
+							<template shadowrootmode="open">
 								<style>
 									:host {
 										display: block;