diff --git a/lib/exceptions/PluginAlreadyLoadingException.php b/lib/exceptions/PluginAlreadyLoadingException.php
index 3a6645f6bee729706ef849a487dd59a66c99c386..e939a1911cb49f8783a7af34ab48d8b69aebefd2 100644
--- a/lib/exceptions/PluginAlreadyLoadingException.php
+++ b/lib/exceptions/PluginAlreadyLoadingException.php
@@ -7,7 +7,7 @@
  */
 class PluginAlreadyLoadingException extends Exception
 {
-    public function __construct($pluginClassName)
+    public function __construct(string $pluginClassName)
     {
         return parent::__construct(
             sprintf(