diff --git a/lib/common/error_codes.js b/lib/common/error_codes.js
index 1459fd940..689cebe38 100644
--- a/lib/common/error_codes.js
+++ b/lib/common/error_codes.js
@@ -14,5 +14,8 @@ module.exports = {
     eofBeforeEndTagName: 'eof-before-end-tag-name',
     cdataInHtmlContent: 'cdata-in-html-content',
     malformedComment: 'malformed-comment',
-    eofInScriptHtmlComment: 'eof-in-script-html-comment'
+    eofInScriptHtmlComment: 'eof-in-script-html-comment',
+    nestedComment: 'nested-comment',
+    abruptComment: 'abrupt-comment',
+    eofInComment: 'eof-in-comment'
 };
diff --git a/lib/tokenizer/index.js b/lib/tokenizer/index.js
index 00660674a..3112e6c44 100644
--- a/lib/tokenizer/index.js
+++ b/lib/tokenizer/index.js
@@ -71,6 +71,10 @@ var DATA_STATE = 'DATA_STATE',
     COMMENT_START_STATE = 'COMMENT_START_STATE',
     COMMENT_START_DASH_STATE = 'COMMENT_START_DASH_STATE',
     COMMENT_STATE = 'COMMENT_STATE',
+    COMMENT_LESS_THAN_SIGN_STATE = 'COMMENT_LESS_THAN_SIGN_STATE',
+    COMMENT_LESS_THAN_SIGN_BANG_STATE = 'COMMENT_LESS_THAN_SIGN_BANG_STATE',
+    COMMENT_LESS_THAN_SIGN_BANG_DASH_STATE = 'COMMENT_LESS_THAN_SIGN_BANG_DASH_STATE',
+    COMMENT_LESS_THAN_SIGN_BANG_DASH_DASH_STATE = 'COMMENT_LESS_THAN_SIGN_BANG_DASH_DASH_STATE',
     COMMENT_END_DASH_STATE = 'COMMENT_END_DASH_STATE',
     COMMENT_END_STATE = 'COMMENT_END_STATE',
     COMMENT_END_BANG_STATE = 'COMMENT_END_BANG_STATE',
@@ -1573,25 +1577,14 @@ _[COMMENT_START_STATE] = function commentStartState(cp) {
     if (cp === $.HYPHEN_MINUS)
         this.state = COMMENT_START_DASH_STATE;
 
-    else if (cp === $.NULL) {
-        this.currentToken.data += UNICODE.REPLACEMENT_CHARACTER;
-        this.state = COMMENT_STATE;
-    }
-
     else if (cp === $.GREATER_THAN_SIGN) {
+        this._err(ERR.abruptComment);
         this.state = DATA_STATE;
         this._emitCurrentToken();
     }
 
-    else if (cp === $.EOF) {
-        this._emitCurrentToken();
-        this._emitEOFToken();
-    }
-
-    else {
-        this.currentToken.data += toChar(cp);
-        this.state = COMMENT_STATE;
-    }
+    else
+        this._reconsumeInState(COMMENT_STATE);
 };
 
 
@@ -1601,26 +1594,21 @@ _[COMMENT_START_DASH_STATE] = function commentStartDashState(cp) {
     if (cp === $.HYPHEN_MINUS)
         this.state = COMMENT_END_STATE;
 
-    else if (cp === $.NULL) {
-        this.currentToken.data += '-';
-        this.currentToken.data += UNICODE.REPLACEMENT_CHARACTER;
-        this.state = COMMENT_STATE;
-    }
-
     else if (cp === $.GREATER_THAN_SIGN) {
+        this._err(ERR.abruptComment);
         this.state = DATA_STATE;
         this._emitCurrentToken();
     }
 
     else if (cp === $.EOF) {
+        this._err(ERR.eofInComment);
         this._emitCurrentToken();
         this._emitEOFToken();
     }
 
     else {
         this.currentToken.data += '-';
-        this.currentToken.data += toChar(cp);
-        this.state = COMMENT_STATE;
+        this._reconsumeInState(COMMENT_STATE);
     }
 };
 
@@ -1631,10 +1619,18 @@ _[COMMENT_STATE] = function commentState(cp) {
     if (cp === $.HYPHEN_MINUS)
         this.state = COMMENT_END_DASH_STATE;
 
-    else if (cp === $.NULL)
+    else if (cp === $.LESS_THAN_SIGN) {
+        this.currentToken.data += '<';
+        this.state = COMMENT_LESS_THAN_SIGN_STATE;
+    }
+
+    else if (cp === $.NULL) {
+        this._err(ERR.unexpectedNullCharacter);
         this.currentToken.data += UNICODE.REPLACEMENT_CHARACTER;
+    }
 
     else if (cp === $.EOF) {
+        this._err(ERR.eofInComment);
         this._emitCurrentToken();
         this._emitEOFToken();
     }
@@ -1644,18 +1640,60 @@ _[COMMENT_STATE] = function commentState(cp) {
 };
 
 
+// Comment less-than sign state
+//------------------------------------------------------------------
+_[COMMENT_LESS_THAN_SIGN_STATE] = function commentLessThanSignState(cp) {
+    if (cp === $.EXCLAMATION_MARK) {
+        this.currentToken.data += '!';
+        this.state = COMMENT_LESS_THAN_SIGN_BANG_STATE;
+    }
+
+    else if (cp === $.LESS_THAN_SIGN)
+        this.currentToken.data += '!';
+
+    else
+        this._reconsumeInState(COMMENT_STATE);
+};
+
+
+// Comment less-than sign bang state
+//------------------------------------------------------------------
+_[COMMENT_LESS_THAN_SIGN_BANG_STATE] = function commentLessThanSignBangState(cp) {
+    if (cp === $.HYPHEN_MINUS)
+        this.state = COMMENT_LESS_THAN_SIGN_BANG_DASH_STATE;
+
+    else
+        this._reconsumeInState(COMMENT_STATE);
+};
+
+
+// Comment less-than sign bang dash state
+//------------------------------------------------------------------
+_[COMMENT_LESS_THAN_SIGN_BANG_DASH_STATE] = function commentLessThanSignBangDashState(cp) {
+    if (cp === $.HYPHEN_MINUS)
+        this.state = COMMENT_LESS_THAN_SIGN_BANG_DASH_DASH_STATE;
+
+    else
+        this._reconsumeInState(COMMENT_END_DASH_STATE);
+};
+
+
+// Comment less-than sign bang dash dash state
+//------------------------------------------------------------------
+_[COMMENT_LESS_THAN_SIGN_BANG_DASH_DASH_STATE] = function commentLessThanSignBangDashDashState(cp) {
+    if (cp !== $.GREATER_THAN_SIGN && cp !== $.EOF)
+        this._err(ERR.nestedComment);
+
+    this._reconsumeInState(COMMENT_END_STATE);
+};
+
+
 // Comment end dash state
 //------------------------------------------------------------------
 _[COMMENT_END_DASH_STATE] = function commentEndDashState(cp) {
     if (cp === $.HYPHEN_MINUS)
         this.state = COMMENT_END_STATE;
 
-    else if (cp === $.NULL) {
-        this.currentToken.data += '-';
-        this.currentToken.data += UNICODE.REPLACEMENT_CHARACTER;
-        this.state = COMMENT_STATE;
-    }
-
     else if (cp === $.EOF) {
         this._emitCurrentToken();
         this._emitEOFToken();
@@ -1663,8 +1701,7 @@ _[COMMENT_END_DASH_STATE] = function commentEndDashState(cp) {
 
     else {
         this.currentToken.data += '-';
-        this.currentToken.data += toChar(cp);
-        this.state = COMMENT_STATE;
+        this._reconsumeInState(COMMENT_STATE);
     }
 };
 
@@ -1683,12 +1720,6 @@ _[COMMENT_END_STATE] = function commentEndState(cp) {
     else if (cp === $.HYPHEN_MINUS)
         this.currentToken.data += '-';
 
-    else if (cp === $.NULL) {
-        this.currentToken.data += '--';
-        this.currentToken.data += UNICODE.REPLACEMENT_CHARACTER;
-        this.state = COMMENT_STATE;
-    }
-
     else if (cp === $.EOF) {
         this._emitCurrentToken();
         this._emitEOFToken();
@@ -1696,8 +1727,7 @@ _[COMMENT_END_STATE] = function commentEndState(cp) {
 
     else {
         this.currentToken.data += '--';
-        this.currentToken.data += toChar(cp);
-        this.state = COMMENT_STATE;
+        this._reconsumeInState(COMMENT_STATE);
     }
 };
 
@@ -1715,12 +1745,6 @@ _[COMMENT_END_BANG_STATE] = function commentEndBangState(cp) {
         this._emitCurrentToken();
     }
 
-    else if (cp === $.NULL) {
-        this.currentToken.data += '--!';
-        this.currentToken.data += UNICODE.REPLACEMENT_CHARACTER;
-        this.state = COMMENT_STATE;
-    }
-
     else if (cp === $.EOF) {
         this._emitCurrentToken();
         this._emitEOFToken();
@@ -1728,8 +1752,7 @@ _[COMMENT_END_BANG_STATE] = function commentEndBangState(cp) {
 
     else {
         this.currentToken.data += '--!';
-        this.currentToken.data += toChar(cp);
-        this.state = COMMENT_STATE;
+        this._reconsumeInState(COMMENT_STATE);
     }
 };