diff --git a/src/Extend/Compat.php b/src/Extend/Compat.php
new file mode 100644
index 000000000..3678f2a84
--- /dev/null
+++ b/src/Extend/Compat.php
@@ -0,0 +1,38 @@
+<?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;
+
+/**
+ * This class is used to wrap old bootstrap.php closures (as used in versions up
+ * to 0.1.0-beta7) in the new Extender format.
+ *
+ * This gives extensions the chance to work with the new API without making any
+ * changes, and have some time to convert to the pure usage of extenders.
+ *
+ * @deprecated
+ */
+class Compat implements Extender
+{
+    protected $callback;
+
+    public function __construct($callback)
+    {
+        $this->callback = $callback;
+    }
+
+    public function apply(Container $container)
+    {
+        $container->call($this->callback);
+    }
+}
diff --git a/src/Extend/Extender.php b/src/Extend/Extender.php
new file mode 100644
index 000000000..71274391e
--- /dev/null
+++ b/src/Extend/Extender.php
@@ -0,0 +1,19 @@
+<?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/Extension/Extension.php b/src/Extension/Extension.php
index 1abb6febe..255a7c6df 100644
--- a/src/Extension/Extension.php
+++ b/src/Extension/Extension.php
@@ -231,6 +231,11 @@ class Extension implements Arrayable
         return $this->path;
     }
 
+    public function getBootstrapperPath()
+    {
+        return "{$this->path}/bootstrap.php";
+    }
+
     /**
      * Tests whether the extension has assets.
      *
diff --git a/src/Extension/ExtensionManager.php b/src/Extension/ExtensionManager.php
index 404638fd5..ad0df4278 100644
--- a/src/Extension/ExtensionManager.php
+++ b/src/Extension/ExtensionManager.php
@@ -12,6 +12,7 @@
 namespace Flarum\Extension;
 
 use Flarum\Database\Migrator;
+use Flarum\Extend\Compat;
 use Flarum\Extension\Event\Disabled;
 use Flarum\Extension\Event\Disabling;
 use Flarum\Extension\Event\Enabled;
@@ -273,21 +274,30 @@ class ExtensionManager
     }
 
     /**
-     * Loads all bootstrap.php files of the enabled extensions.
+     * Retrieve all extender instances of all enabled extensions.
      *
      * @return Collection
      */
-    public function getEnabledBootstrappers()
+    public function getActiveExtenders()
     {
-        $bootstrappers = new Collection;
+        return $this->getEnabledExtensions()
+            ->flatMap(function (Extension $extension) {
+                $bootstrapper = $extension->getBootstrapperPath();
+                if ($this->filesystem->exists($bootstrapper)) {
+                    $extenders = require $bootstrapper;
 
-        foreach ($this->getEnabledExtensions() as $extension) {
-            if ($this->filesystem->exists($file = $extension->getPath().'/bootstrap.php')) {
-                $bootstrappers->push($file);
-            }
-        }
+                    if (is_array($extenders)) {
+                        return $extenders;
+                    }
 
-        return $bootstrappers;
+                    // Assume that the extension has not yet switched to the new
+                    // bootstrap.php format, and wrap the callback in a Compat
+                    // extender.
+                    return [new Compat($extenders)];
+                } else {
+                    return [];
+                }
+            });
     }
 
     /**
diff --git a/src/Extension/ExtensionServiceProvider.php b/src/Extension/ExtensionServiceProvider.php
index 77b88d3e5..78b8be201 100644
--- a/src/Extension/ExtensionServiceProvider.php
+++ b/src/Extension/ExtensionServiceProvider.php
@@ -12,6 +12,7 @@
 namespace Flarum\Extension;
 
 use Flarum\Foundation\AbstractServiceProvider;
+use Illuminate\Contracts\Container\Container;
 
 class ExtensionServiceProvider extends AbstractServiceProvider
 {
@@ -22,13 +23,14 @@ class ExtensionServiceProvider extends AbstractServiceProvider
     {
         $this->app->bind('flarum.extensions', ExtensionManager::class);
 
-        $bootstrappers = $this->app->make('flarum.extensions')->getEnabledBootstrappers();
+        $this->app->booting(function (Container $app) {
+            /** @var \Flarum\Extend\Extender[] $extenders */
+            $extenders = $app->make('flarum.extensions')->getActiveExtenders();
 
-        foreach ($bootstrappers as $file) {
-            $bootstrapper = require $file;
-
-            $this->app->call($bootstrapper);
-        }
+            foreach ($extenders as $extender) {
+                $extender->apply($app);
+            }
+        });
     }
 
     /**