diff --git a/src/GeshiFilterCss.php b/src/GeshiFilterCss.php
index a49507c..dd1152b 100644
--- a/src/GeshiFilterCss.php
+++ b/src/GeshiFilterCss.php
@@ -104,10 +104,10 @@ class GeshiFilterCss {
 
       $ret = file_save_data($stylesheet, $stylesheet_filename, FILE_EXISTS_REPLACE);
       if ($ret) {
-        drupal_set_message(t('(Re)generated external CSS style sheet %file.', array('%file' => $ret->getFilename())));
+        drupal_set_message($this->t('(Re)generated external CSS style sheet %file.', array('%file' => $ret->getFilename())));
       }
       else {
-        drupal_set_message($t('Could not generate external CSS file. Check the settings of your <a href="!filesystem">file system</a>.',
+        drupal_set_message($this->t('Could not generate external CSS file. Check the settings of your <a href="!filesystem">file system</a>.',
           array(
             '!filesystem' => Url::fromRoute('system.file_system_settings')->toString(),
           )), 'error');