diff --git a/extension.json b/extension.json
index 9fce6fcce..6dabe2bbd 100644
--- a/extension.json
+++ b/extension.json
@@ -68,6 +68,7 @@
 				"mediawiki.Uri",
 				"mediawiki.util",
 				"mediawiki.storage",
+				"mediawiki.String",
 				"ext.visualEditor.core.utils.parsing"
 			],
 			"messages": [
diff --git a/includes/CommentParser.php b/includes/CommentParser.php
index 00587eb8c..9ed88690e 100644
--- a/includes/CommentParser.php
+++ b/includes/CommentParser.php
@@ -511,7 +511,7 @@ class CommentParser {
 			( $node = $node->previousSibling ) && $length < self::SIGNATURE_SCAN_LIMIT && $node !== $until
 		) {
 			$sigNodes[] = $node;
-			$length += $node->textContent ? strlen( $node->textContent ) : 0;
+			$length += $node->textContent ? mb_strlen( $node->textContent ) : 0;
 			if ( !( $node instanceof DOMElement ) ) {
 				continue;
 			}
diff --git a/modules/Parser.js b/modules/Parser.js
index 781027d53..b76b1a72b 100644
--- a/modules/Parser.js
+++ b/modules/Parser.js
@@ -7,6 +7,7 @@
 
 var
 	utils = require( './utils.js' ),
+	codePointLength = require( 'mediawiki.String' ).codePointLength,
 	CommentItem = require( './CommentItem.js' ),
 	HeadingItem = require( './HeadingItem.js' ),
 	// Hooks::getLocalData()
@@ -530,7 +531,7 @@ Parser.prototype.findSignature = function ( timestampNode, until ) {
 
 	while ( ( node = node.previousSibling ) && length < data.signatureScanLimit && node !== until ) {
 		sigNodes.push( node );
-		length += ( node.textContent || '' ).length;
+		length += node.textContent ? codePointLength( node.textContent ) : 0;
 		if ( node.nodeType !== Node.ELEMENT_NODE ) {
 			continue;
 		}