diff --git a/lib/base.php b/lib/base.php
index fb58177a43..badbe3cd1f 100644
--- a/lib/base.php
+++ b/lib/base.php
@@ -103,6 +103,9 @@ class OC {
 	 */
 	public static $loader = null;
 
+	/** @var \Composer\Autoload\ClassLoader $composerAutoloader */
+	public static $composerAutoloader = null;
+
 	/**
 	 * @var \OC\Server
 	 */
@@ -493,7 +496,7 @@ class OC {
 		self::$CLI = (php_sapi_name() == 'cli');
 
 		// Add default composer PSR-4 autoloader
-		require_once OC::$SERVERROOT . '/lib/composer/autoload.php';
+		self::$composerAutoloader = require_once OC::$SERVERROOT . '/lib/composer/autoload.php';
 
 		try {
 			self::initPaths();
diff --git a/lib/private/legacy/app.php b/lib/private/legacy/app.php
index 41b1b79e4f..fe590e4159 100644
--- a/lib/private/legacy/app.php
+++ b/lib/private/legacy/app.php
@@ -108,7 +108,7 @@ class OC_App {
 		foreach($apps as $app) {
 			$path = self::getAppPath($app);
 			if($path !== false) {
-				\OC::$loader->addValidRoot($path);
+				self::registerAutoloading($app, $path);
 			}
 		}
 
@@ -137,7 +137,10 @@ class OC_App {
 		if($appPath === false) {
 			return;
 		}
-		\OC::$loader->addValidRoot($appPath); // in case someone calls loadApp() directly
+
+		// in case someone calls loadApp() directly
+		self::registerAutoloading($app, $appPath);
+
 		if (is_file($appPath . '/appinfo/app.php')) {
 			\OC::$server->getEventLogger()->start('load_app_' . $app, 'Load app: ' . $app);
 			if ($checkUpgrade and self::shouldUpgrade($app)) {
@@ -155,6 +158,22 @@ class OC_App {
 		}
 	}
 
+	/**
+	 * @param string $app
+	 * @param string $path
+	 */
+	protected static function registerAutoloading($app, $path) {
+		// Register on PSR-4 composer autoloader
+		$appNamespace = \OC\AppFramework\App::buildAppNamespace($app);
+		\OC::$composerAutoloader->addPsr4($appNamespace . '\\', $path . '/lib/', true);
+		if (defined('PHPUNIT_RUN')) {
+			\OC::$composerAutoloader->addPsr4($appNamespace . '\\Tests\\', $path . '/tests/', true);
+		}
+
+		// Register on legacy autoloader
+		\OC::$loader->addValidRoot($path);
+	}
+
 	/**
 	 * Load app.php from the given app
 	 *