diff --git a/extensions/tags/bootstrap.php b/extensions/tags/bootstrap.php
index 51ea032cf..2f78404cb 100644
--- a/extensions/tags/bootstrap.php
+++ b/extensions/tags/bootstrap.php
@@ -6,4 +6,4 @@ require __DIR__.'/vendor/autoload.php';
 
 // Register our service provider with the Flarum application. In here we can
 // register bindings and execute code when the application boots.
-return $app->register('Flarum\Categories\CategoriesServiceProvider');
+return $this->app->register('Flarum\Categories\CategoriesServiceProvider');