diff --git a/lib/private/Installer.php b/lib/private/Installer.php
index 8702f264e5..35f51b19b0 100644
--- a/lib/private/Installer.php
+++ b/lib/private/Installer.php
@@ -98,7 +98,7 @@ class Installer {
 	 *
 	 * @param string $appId App to install
 	 * @throws \Exception
-	 * @return integer
+	 * @return string app ID
 	 */
 	public function installApp($appId) {
 		$app = \OC_App::findAppInDirectories($appId);
@@ -109,6 +109,29 @@ class Installer {
 		$basedir = $app['path'].'/'.$appId;
 		$info = OC_App::getAppInfo($basedir.'/appinfo/info.xml', true);
 
+		$l = \OC::$server->getL10N('core');
+
+		if(!is_array($info)) {
+			throw new \Exception(
+				$l->t('App "%s" cannot be installed because appinfo file cannot be read.',
+					[$info['name']]
+				)
+			);
+		}
+
+		$version = \OCP\Util::getVersion();
+		if (!\OC_App::isAppCompatible($version, $info)) {
+			throw new \Exception(
+				// TODO $l
+				$l->t('App "%s" cannot be installed because it is not compatible with this version of the server.',
+					[$info['name']]
+				)
+			);
+		}
+
+		// check for required dependencies
+		\OC_App::checkAppDependencies($this->config, $l, $info);
+
 		//install the database
 		if(is_file($basedir.'/appinfo/database.xml')) {
 			if (\OC::$server->getAppConfig()->getValue($info['id'], 'installed_version') === null) {
@@ -120,6 +143,9 @@ class Installer {
 
 		\OC_App::registerAutoloading($appId, $basedir);
 		\OC_App::setupBackgroundJobs($info['background-jobs']);
+		if(isset($info['settings']) && is_array($info['settings'])) {
+			\OC::$server->getSettingsManager()->setupSettings($info['settings']);
+		}
 
 		//run appinfo/install.php
 		if((!isset($data['noinstall']) or $data['noinstall']==false)) {
diff --git a/lib/private/legacy/app.php b/lib/private/legacy/app.php
index 111da7d0d4..2e9e97d5bd 100644
--- a/lib/private/legacy/app.php
+++ b/lib/private/legacy/app.php
@@ -357,8 +357,6 @@ class OC_App {
 	public function enable($appId,
 						   $groups = null) {
 		self::$enabledAppsCache = []; // flush
-		$l = \OC::$server->getL10N('core');
-		$config = \OC::$server->getConfig();
 
 		// Check if app is already downloaded
 		$installer = new Installer(
@@ -374,23 +372,7 @@ class OC_App {
 			$installer->downloadApp($appId);
 		}
 
-		if (!Installer::isInstalled($appId)) {
-			$appId = self::installApp(
-				$appId,
-				$config,
-				$l
-			);
-			$appPath = self::getAppPath($appId);
-			self::registerAutoloading($appId, $appPath);
-			$installer->installApp($appId);
-		} else {
-			// check for required dependencies
-			$info = self::getAppInfo($appId);
-			self::checkAppDependencies($config, $l, $info);
-			$appPath = self::getAppPath($appId);
-			self::registerAutoloading($appId, $appPath);
-			$installer->installApp($appId);
-		}
+		$installer->installApp($appId);
 
 		$appManager = \OC::$server->getAppManager();
 		if (!is_null($groups)) {
@@ -406,13 +388,6 @@ class OC_App {
 		} else {
 			$appManager->enableApp($appId);
 		}
-
-		$info = self::getAppInfo($appId);
-		if(isset($info['settings']) && is_array($info['settings'])) {
-			$appPath = self::getAppPath($appId);
-			self::registerAutoloading($appId, $appPath);
-			\OC::$server->getSettingsManager()->setupSettings($info['settings']);
-		}
 	}
 
 	/**
@@ -1258,7 +1233,7 @@ class OC_App {
 	 * @param array $info
 	 * @throws \Exception
 	 */
-	protected static function checkAppDependencies($config, $l, $info) {
+	public static function checkAppDependencies($config, $l, $info) {
 		$dependencyAnalyzer = new DependencyAnalyzer(new Platform($config), $l);
 		$missing = $dependencyAnalyzer->analyze($info);
 		if (!empty($missing)) {
diff --git a/settings/ajax/installapp.php b/settings/ajax/installapp.php
deleted file mode 100644
index 17e5eadf50..0000000000
--- a/settings/ajax/installapp.php
+++ /dev/null
@@ -1,52 +0,0 @@
-<?php
-/**
- * @copyright Copyright (c) 2016, ownCloud, Inc.
- *
- * @author Georg Ehrke <georg@owncloud.com>
- * @author Lukas Reschke <lukas@statuscode.ch>
- * @author Robin Appelman <robin@icewind.nl>
- *
- * @license AGPL-3.0
- *
- * This code is free software: you can redistribute it and/or modify
- * it under the terms of the GNU Affero General Public License, version 3,
- * as published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU Affero General Public License for more details.
- *
- * You should have received a copy of the GNU Affero General Public License, version 3,
- * along with this program.  If not, see <http://www.gnu.org/licenses/>
- *
- */
-OCP\JSON::checkAdminUser();
-OCP\JSON::callCheck();
-
-$lastConfirm = (int) \OC::$server->getSession()->get('last-password-confirm');
-if ($lastConfirm < (time() - 30 * 60 + 15)) { // allow 15 seconds delay
-	$l = \OC::$server->getL10N('core');
-	OC_JSON::error(array( 'data' => array( 'message' => $l->t('Password confirmation is required'))));
-	exit();
-}
-
-if (!array_key_exists('appid', $_POST)) {
-	OC_JSON::error();
-	exit;
-}
-
-$app = new OC_App();
-$appId = (string)$_POST['appid'];
-$appId = OC_App::cleanAppId($appId);
-$result = $app->installApp(
-	$appId,
-	\OC::$server->getConfig(),
-	\OC::$server->getL10N('core')
-);
-if($result !== false) {
-	OC_JSON::success(array('data' => array('appid' => $appId)));
-} else {
-	$l = \OC::$server->getL10N('settings');
-	OC_JSON::error(array("data" => array( "message" => $l->t("Couldn't remove app.") )));
-}