diff --git a/lib/classes/output/mustache_shorten_text_helper.php b/lib/classes/output/mustache_shorten_text_helper.php
index 16bb1a7d84b..8a470647903 100644
--- a/lib/classes/output/mustache_shorten_text_helper.php
+++ b/lib/classes/output/mustache_shorten_text_helper.php
@@ -55,8 +55,9 @@ class mustache_shorten_text_helper {
         $length = trim($length);
         $text = trim($text);
 
-        // Allow mustache tags in the text.
+        // Allow mustache tags in the length and text.
         $text = $helper->render($text);
+        $length = $helper->render($length);
 
         return shorten_text($text, $length);
     }