diff --git a/src/Extend/Assets.php b/src/Extend/Assets.php
index 6fb52dbd7..b09654aba 100644
--- a/src/Extend/Assets.php
+++ b/src/Extend/Assets.php
@@ -15,7 +15,7 @@ use Flarum\Frontend\Event\Rendering;
 use Illuminate\Contracts\Container\Container;
 use Illuminate\Events\Dispatcher;
 
-class Assets implements Extender
+class Assets
 {
     protected $appName;
 
@@ -49,7 +49,7 @@ class Assets implements Extender
         return $this;
     }
 
-    public function apply(Container $container)
+    public function __invoke(Container $container)
     {
         $container->make(Dispatcher::class)->listen(
             Rendering::class,
diff --git a/src/Extend/Compat.php b/src/Extend/Compat.php
index 3678f2a84..469729b5b 100644
--- a/src/Extend/Compat.php
+++ b/src/Extend/Compat.php
@@ -22,7 +22,7 @@ use Illuminate\Contracts\Container\Container;
  *
  * @deprecated
  */
-class Compat implements Extender
+class Compat
 {
     protected $callback;
 
@@ -31,7 +31,7 @@ class Compat implements Extender
         $this->callback = $callback;
     }
 
-    public function apply(Container $container)
+    public function __invoke(Container $container)
     {
         $container->call($this->callback);
     }
diff --git a/src/Extend/Extender.php b/src/Extend/Extender.php
deleted file mode 100644
index 71274391e..000000000
--- a/src/Extend/Extender.php
+++ /dev/null
@@ -1,19 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * (c) Toby Zerner <toby.zerner@gmail.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Flarum\Extend;
-
-use Illuminate\Contracts\Container\Container;
-
-interface Extender
-{
-    public function apply(Container $container);
-}
diff --git a/src/Extend/FormatterConfiguration.php b/src/Extend/FormatterConfiguration.php
index 1608a35fd..ad6ca0ab7 100644
--- a/src/Extend/FormatterConfiguration.php
+++ b/src/Extend/FormatterConfiguration.php
@@ -15,7 +15,7 @@ use Flarum\Formatter\Event\Configuring;
 use Illuminate\Contracts\Container\Container;
 use Illuminate\Events\Dispatcher;
 
-class FormatterConfiguration implements Extender
+class FormatterConfiguration
 {
     protected $callback;
 
@@ -24,7 +24,7 @@ class FormatterConfiguration implements Extender
         $this->callback = $callback;
     }
 
-    public function apply(Container $container)
+    public function __invoke(Container $container)
     {
         $container->make(Dispatcher::class)->listen(
             Configuring::class,
diff --git a/src/Extend/Locale.php b/src/Extend/Locale.php
index 08e126b41..916e9da88 100644
--- a/src/Extend/Locale.php
+++ b/src/Extend/Locale.php
@@ -16,7 +16,7 @@ use Flarum\Locale\LocaleManager;
 use Illuminate\Contracts\Container\Container;
 use RuntimeException;
 
-class Locale implements Extender
+class Locale
 {
     protected $directory;
 
@@ -25,7 +25,7 @@ class Locale implements Extender
         $this->directory = $directory;
     }
 
-    public function apply(Container $container)
+    public function __invoke(Container $container)
     {
         $this->loadLanguagePackFrom(
             $this->directory,
diff --git a/src/Extend/Routes.php b/src/Extend/Routes.php
index c8dda4255..c02ff92eb 100644
--- a/src/Extend/Routes.php
+++ b/src/Extend/Routes.php
@@ -14,7 +14,7 @@ namespace Flarum\Extend;
 use Flarum\Http\RouteHandlerFactory;
 use Illuminate\Contracts\Container\Container;
 
-class Routes implements Extender
+class Routes
 {
     protected $appName;
 
@@ -62,7 +62,7 @@ class Routes implements Extender
         return $this;
     }
 
-    public function apply(Container $container)
+    public function __invoke(Container $container)
     {
         if (empty($this->routes)) {
             return;
diff --git a/src/Extension/ExtensionServiceProvider.php b/src/Extension/ExtensionServiceProvider.php
index 78b8be201..2e484bfbc 100644
--- a/src/Extension/ExtensionServiceProvider.php
+++ b/src/Extension/ExtensionServiceProvider.php
@@ -24,11 +24,11 @@ class ExtensionServiceProvider extends AbstractServiceProvider
         $this->app->bind('flarum.extensions', ExtensionManager::class);
 
         $this->app->booting(function (Container $app) {
-            /** @var \Flarum\Extend\Extender[] $extenders */
+            /** @var callable[] $extenders */
             $extenders = $app->make('flarum.extensions')->getActiveExtenders();
 
             foreach ($extenders as $extender) {
-                $extender->apply($app);
+                $app->call($extender);
             }
         });
     }