diff --git a/app/vendor/ParsedownExtra.php b/app/vendor/ParsedownExtra.php
index d192e2b..2adcbaa 100644
--- a/app/vendor/ParsedownExtra.php
+++ b/app/vendor/ParsedownExtra.php
@@ -508,7 +508,7 @@ class ParsedownExtra extends Parsedown
             ),
         );
 
-        uasort($this->DefinitionData['Footnote'], 'self::sortFootnotes');
+        uasort($this->DefinitionData['Footnote'], [$this, 'sortFootnotes']);
 
         foreach ($this->DefinitionData['Footnote'] as $definitionId => $DefinitionData)
         {