diff --git a/frontends/php/include/events.inc.php b/frontends/php/include/events.inc.php
index 3b876ed..c5a539b 100644
--- a/frontends/php/include/events.inc.php
+++ b/frontends/php/include/events.inc.php
@@ -558,7 +558,7 @@ function getTagString(array $tag, $tag_name_format = PROBLEMS_TAG_NAME_FULL) {
 			return $tag['value'];
 
 		case PROBLEMS_TAG_NAME_SHORTENED:
-			return substr($tag['tag'], 0, 3).(($tag['value'] === '') ? '' : ': '.$tag['value']);
+			return mb_substr($tag['tag'], 0, 3).(($tag['value'] === '') ? '' : ': '.$tag['value']);
 
 		default:
 			return $tag['tag'].(($tag['value'] === '') ? '' : ': '.$tag['value']);