diff --git a/src/parse/state/tag.js b/src/parse/state/tag.js
index 2db102ab0d..72f73f0651 100644
--- a/src/parse/state/tag.js
+++ b/src/parse/state/tag.js
@@ -6,7 +6,7 @@ import { trimStart, trimEnd } from '../utils/trim.js';
 import { decodeCharacterReferences } from '../utils/html.js';
 import voidElementNames from '../../utils/voidElementNames.js';
 
-const validTagName = /^[a-zA-Z]{1,}:?[a-zA-Z0-9\-]*/;
+const validTagName = /^\!?[a-zA-Z]{1,}:?[a-zA-Z0-9\-]*/;
 const invalidUnquotedAttributeCharacters = /[\s"'=<>\/`]/;
 
 const specials = {
diff --git a/src/utils/voidElementNames.js b/src/utils/voidElementNames.js
index 7df1d452b6..46306ac8c3 100644
--- a/src/utils/voidElementNames.js
+++ b/src/utils/voidElementNames.js
@@ -1 +1 @@
-export default /^(?:area|base|br|col|command|doctype|embed|hr|img|input|keygen|link|meta|param|source|track|wbr)$/;
+export default /^(?:area|base|br|col|command|\!doctype|embed|hr|img|input|keygen|link|meta|param|source|track|wbr)$/;