diff --git a/packages/happy-dom/src/xml-parser/XMLParser.ts b/packages/happy-dom/src/xml-parser/XMLParser.ts
index ccf5d3084..04e1fed1a 100755
--- a/packages/happy-dom/src/xml-parser/XMLParser.ts
+++ b/packages/happy-dom/src/xml-parser/XMLParser.ts
@@ -24,7 +24,7 @@ import HTMLElementConfigContentModelEnum from '../config/HTMLElementConfigConten
  * Group 8: End of start tag (e.g. ">" in "<div>").
  */
 const MARKUP_REGEXP =
-	/<([a-zA-Z0-9-]+)|<\/([a-zA-Z0-9-]+)\s*>|<!--([^-]+)-->|<!--([^>]+)>|<!([^>]+)>|<\?([^>]+)>|(\/>)|(>)/gm;
+	/<([a-zA-Z0-9-]+)|<\/([a-zA-Z0-9-]+)\s*>|<!--([^-]+)-->|<!--([^>]+)>|<!([^>]*)>|<\?([^>]+)>|(\/>)|(>)/gm;
 
 /**
  * Attribute RegExp.
@@ -95,7 +95,7 @@ export default class XMLParser {
 					case MarkupReadStateEnum.startOrEndTag:
 						if (
 							match.index !== lastIndex &&
-							(match[1] || match[2] || match[3] || match[4] || match[5] || match[6])
+							(match[1] || match[2] || match[3] || match[4] || match[5] !== undefined || match[6])
 						) {
 							// Plain text between tags.
 
@@ -181,9 +181,9 @@ export default class XMLParser {
 							}
 
 							currentNode.appendChild(document.createComment(Entities.decodeHTML(comment)));
-						} else if (match[5]) {
-							// Exclamation mark comment (usually <!DOCTYPE>).
-
+						} else if (match[5] !== undefined) {
+							// Exclamation mark comment.
+							// Document type node or comment.
 							const exclamationComment = Entities.decodeHTML(match[5]);
 							currentNode.appendChild(
 								this.getDocumentTypeNode(document, exclamationComment) ||
diff --git a/packages/happy-dom/test/custom-element/CustomElementRegistry.test.ts b/packages/happy-dom/test/custom-element/CustomElementRegistry.test.ts
index 2d17034d2..3f3b81cac 100644
--- a/packages/happy-dom/test/custom-element/CustomElementRegistry.test.ts
+++ b/packages/happy-dom/test/custom-element/CustomElementRegistry.test.ts
@@ -2,7 +2,6 @@ import CustomElement from '../CustomElement.js';
 import CustomElementRegistry from '../../src/custom-element/CustomElementRegistry.js';
 import Window from '../../src/window/Window.js';
 import Document from '../../src/nodes/document/Document.js';
-import Window from '../../src/window/Window.js';
 import DOMException from '../../src/exception/DOMException.js';
 import { beforeEach, describe, it, expect } from 'vitest';
 import * as PropertySymbol from '../../src/PropertySymbol.js';
diff --git a/packages/happy-dom/test/xml-parser/XMLParser.test.ts b/packages/happy-dom/test/xml-parser/XMLParser.test.ts
index d4037a608..a0228e36e 100644
--- a/packages/happy-dom/test/xml-parser/XMLParser.test.ts
+++ b/packages/happy-dom/test/xml-parser/XMLParser.test.ts
@@ -16,6 +16,7 @@ const GET_EXPECTED_HTML = (html: string): string =>
 		.replace('<?processing instruction?>', '<!--?processing instruction?-->')
 		.replace('<?processing-instruction>', '<!--?processing-instruction-->')
 		.replace('<!Exclamation mark comment>', '<!--Exclamation mark comment-->')
+		.replace('<!>', '<!---->')
 		.replace('<!DOCTYPE HTML', '<!DOCTYPE html')
 		.replace('<img />', '<img>');
 
diff --git a/packages/happy-dom/test/xml-parser/data/XMLParserHTML.ts b/packages/happy-dom/test/xml-parser/data/XMLParserHTML.ts
index cfc0bafb0..fea879fc1 100644
--- a/packages/happy-dom/test/xml-parser/data/XMLParserHTML.ts
+++ b/packages/happy-dom/test/xml-parser/data/XMLParserHTML.ts
@@ -13,6 +13,7 @@ export default `
 				<b>Bold</b>
 				<!-- Comment 2 !-->
 				<span>Span</span>
+                <!>
 			</div>
 			<article class="class1 class2" id="id">
 				<!-- Comment 1 !-->
