diff --git a/lib/classes/StudipCoreFormat.php b/lib/classes/StudipCoreFormat.php
index 871f5fa28512b7509a3e1d78eb7de3570b393a18..b6562527df5d51835d3e7061d69813e89c0f3bc0 100644
--- a/lib/classes/StudipCoreFormat.php
+++ b/lib/classes/StudipCoreFormat.php
@@ -473,7 +473,7 @@ class StudipCoreFormat extends TextFormat
      */
     protected static function markupQuote($markup, $matches, $contents)
     {
-        if (mb_strlen($matches[1]) > 1) {
+        if (isset($matches[1]) && mb_strlen($matches[1]) > 1) {
             $title = sprintf(_('%s hat geschrieben:'), $markup->format(mb_substr($matches[1], 1)));
             return sprintf('<blockquote><div class="author">%s</div>%s</blockquote>',
                        $title, trim($contents));