diff --git a/lib/common/error_codes.js b/lib/common/error_codes.js
index da156daf1..1459fd940 100644
--- a/lib/common/error_codes.js
+++ b/lib/common/error_codes.js
@@ -10,6 +10,7 @@ module.exports = {
     startOfProcessingInstructionOrXMLDeclaration: 'start-of-processing-instruction-or-xml-declaration',
     unexpectedFirstCharacterOfStartTagName: 'unexpected-first-character-of-start-tag-name',
     missingEndTagName: 'missing-end-tag-name',
+    eofInTagName: 'eof-in-tag-name',
     eofBeforeEndTagName: 'eof-before-end-tag-name',
     cdataInHtmlContent: 'cdata-in-html-content',
     malformedComment: 'malformed-comment',
diff --git a/lib/tokenizer/index.js b/lib/tokenizer/index.js
index e67612e9a..00660674a 100644
--- a/lib/tokenizer/index.js
+++ b/lib/tokenizer/index.js
@@ -748,11 +748,15 @@ _[TAG_NAME_STATE] = function tagNameState(cp) {
     else if (isAsciiUpper(cp))
         this.currentToken.tagName += toAsciiLowerChar(cp);
 
-    else if (cp === $.NULL)
+    else if (cp === $.NULL) {
+        this._err(ERR.unexpectedNullCharacter);
         this.currentToken.tagName += UNICODE.REPLACEMENT_CHARACTER;
+    }
 
-    else if (cp === $.EOF)
+    else if (cp === $.EOF) {
+        this._err(ERR.eofInTagName);
         this._emitEOFToken();
+    }
 
     else
         this.currentToken.tagName += toChar(cp);