diff --git a/Sources/Config.php b/Sources/Config.php
index 2228391bbb9..d58179849f2 100644
--- a/Sources/Config.php
+++ b/Sources/Config.php
@@ -254,6 +254,8 @@ class Config
 	public static string $sourcedir;
 
 	/**
+	 * @var string
+	 *
 	 * Path to where our dependencies are located.
 	 */
 	public static string $vendordir;
@@ -322,6 +324,14 @@ class Config
 	 */
 	public static string $scripturl;
 
+	/**
+	 * @var \Composer\Autoload\ClassLoader
+	 *
+	 * Autoloader instance.
+	 * This is used to support the integrate_autoload hook.
+	 */
+	public static \Composer\Autoload\ClassLoader $loader;
+
 	/****************************
 	 * Internal static properties
 	 ****************************/
@@ -1136,6 +1146,18 @@ public static function reloadModSettings(): void
 			die('SMF file version (' . SMF_VERSION . ') does not match SMF database version (' . self::$modSettings['smfVersion'] . ').<br>Run the SMF upgrader to fix this.<br><a href="https://wiki.simplemachines.org/smf/Upgrading">More information</a>.');
 		}
 
+		// Any autoloader integrations to add?
+		if (isset(self::$modSettings['integrate_autoload'])) {
+			$class_map = [];
+
+			IntegrationHook::call('integrate_autoload', [&$class_map]);
+
+			foreach ($class_map as $prefix => $dirname) {
+				self::$loader->addPsr4($prefix, $dirname);
+			}
+		}
+
+		// Ensure the cache_enable setting reflects reality.
 		self::$modSettings['cache_enable'] = Cache\CacheApi::$enable;
 
 		// Used to force browsers to download fresh CSS and JavaScript when necessary
diff --git a/composer.json b/composer.json
index 37d8ad06929..7c04e8affd7 100644
--- a/composer.json
+++ b/composer.json
@@ -1,35 +1,36 @@
 {
-    "name": "simplemachines/smf",
-    "repositories": [
-        {
-            "url": "https://github.com/SimpleMachines/BuildTools.git",
-            "type": "vcs"
-        }
-    ],
+	"name": "simplemachines/smf",
+	"repositories": [
+		{
+			"url": "https://github.com/SimpleMachines/BuildTools.git",
+			"type": "vcs"
+		}
+	],
 	"autoload": {
 		"psr-4": {
-			"SMF\\": "Sources/"
+			"SMF\\": "Sources/",
+			"SMF\\Themes\\": "Themes/"
+		}
+	},
+	"minimum-stability": "dev",
+	"prefer-stable": true,
+	"require-dev": {
+		"simplemachines/build-tools": "dev-release-3.0",
+		"friendsofphp/php-cs-fixer": "^3.40"
+	},
+	"scripts": {
+		"lint": "php-cs-fixer --quiet check --config .php-cs-fixer.dist.php --path-mode=intersection $(git diff --name-only \"*.php\") || php-cs-fixer check --diff --config .php-cs-fixer.dist.php --path-mode=intersection $(git diff --name-only \"*.php\") --allow-risky=yes",
+		"lint-fix": "php-cs-fixer fix -v --config .php-cs-fixer.dist.php --path-mode=intersection $(git diff --name-only \"*.php\") --allow-risky=yes"
+	},
+	"config": {
+		"platform": {
+			"php": "8.0.0"
 		}
 	},
-    "minimum-stability": "dev",
-    "prefer-stable": true,
-    "require-dev": {
-        "simplemachines/build-tools": "dev-release-3.0",
-        "friendsofphp/php-cs-fixer": "^3.40"
-    },
-    "scripts": {
-        "lint": "php-cs-fixer --quiet check --config .php-cs-fixer.dist.php --path-mode=intersection $(git diff --name-only \"*.php\") || php-cs-fixer check --diff --config .php-cs-fixer.dist.php --path-mode=intersection $(git diff --name-only \"*.php\") --allow-risky=yes",
-        "lint-fix": "php-cs-fixer fix -v --config .php-cs-fixer.dist.php --path-mode=intersection $(git diff --name-only \"*.php\") --allow-risky=yes"
-    },
-    "config": {
-        "platform": {
-            "php": "8.0.0"
-        }
-    },
 	"require": {
 		"google/recaptcha": "^1.3",
 		"matthiasmullie/minify": "^1.3",
 		"bjeavons/zxcvbn-php": "^1.0",
-        "matthiasmullie/path-converter": "^1.1"
+		"matthiasmullie/path-converter": "^1.1"
 	}
 }
diff --git a/index.php b/index.php
index d8169347096..8e07434b717 100644
--- a/index.php
+++ b/index.php
@@ -122,13 +122,11 @@
 	require_once $sourcedir . DIRECTORY_SEPARATOR . 'Config.php';
 	SMF\Config::set(get_defined_vars());
 
-	$loader = require SMF\Config::$vendordir . '/autoload.php';
+	// Start up the autoloader.
+	SMF\Config::$loader = require SMF\Config::$vendordir . '/autoload.php';
 
-	if (isset(SMF\Config::$modSettings['integrate_autoload'])) {
-		foreach (explode(',', SMF\Config::$modSettings['integrate_autoload']) as $prefix => $dirname) {
-			$loader->addPsr4($prefix, $dirname);
-		}
-	}
+	// Ensure the SMF namespace points to $sourcedir.
+	SMF\Config::$loader->setPsr4('SMF\\', $sourcedir);
 
 	// Ensure $db_last_error is set, too.
 	SMF\Config::getDbLastError();
diff --git a/other/Settings.php b/other/Settings.php
index be055e45a89..767ea48a5d9 100644
--- a/other/Settings.php
+++ b/other/Settings.php
@@ -208,6 +208,12 @@
  * Path to the Packages directory.
  */
 $packagesdir = __DIR__ . '/Packages';
+/**
+ * @var string
+ *
+ * Path to where our dependencies are located.
+ */
+$vendordir = __DIR__ . '/vendor';
 /**
  * @var string
  *
diff --git a/other/Settings_bak.php b/other/Settings_bak.php
index e4f02b11f1d..49e242a1ed4 100644
--- a/other/Settings_bak.php
+++ b/other/Settings_bak.php
@@ -208,6 +208,12 @@
  * Path to the Packages directory.
  */
 $packagesdir = __DIR__ . '/Packages';
+/**
+ * @var string
+ *
+ * Path to where our dependencies are located.
+ */
+$vendordir = __DIR__ . '/vendor';
 /**
  * @var string
  *