diff --git a/apps/files_sharing/lib/proxy.php b/apps/files_sharing/lib/proxy.php
index c899a4b4dd372e46a608aa97c69b4d5946ddc12a..f595328cc63f9797528b0d5400fa134eaa1027fe 100644
--- a/apps/files_sharing/lib/proxy.php
+++ b/apps/files_sharing/lib/proxy.php
@@ -57,7 +57,7 @@ class Proxy extends \OC_FileProxy {
 		$mountManager = \OC\Files\Filesystem::getMountManager();
 		$mountedShares = $mountManager->findIn($path);
 		foreach ($mountedShares as $mount) {
-			if ($mount->getStorage() instanceof \OC\Files\Storage\Shared) {
+			if ($mount->getStorage()->instanceOfStorage('\OC\Files\Storage\Shared')) {
 				$mountPoint = $mount->getMountPoint();
 				$mountPointName = $mount->getMountPointName();
 				$target = \OCA\Files_Sharing\Helper::generateUniqueTarget(dirname($path) . '/' . $mountPointName, array(), $view);
diff --git a/apps/files_sharing/lib/sharedstorage.php b/apps/files_sharing/lib/sharedstorage.php
index 67ccbd134035a7a66bdd9d251acc4c87c41f4453..a7dd2b3afa1df6c78a03c484b0d9130a7d0db60c 100644
--- a/apps/files_sharing/lib/sharedstorage.php
+++ b/apps/files_sharing/lib/sharedstorage.php
@@ -300,7 +300,7 @@ class Shared extends \OC\Files\Storage\Common {
 
 		// it shouldn't be possible to move a Shared storage into another one
 		list($targetStorage, ) = \OC\Files\Filesystem::resolvePath($targetPath);
-		if ($targetStorage instanceof \OC\Files\Storage\Shared) {
+		if ($targetStorage->instanceOfStorage('\OC\Files\Storage\Shared')) {
 			\OCP\Util::writeLog('file sharing',
 					'It is not allowed to move one mount point into another one',
 					\OCP\Util::DEBUG);
diff --git a/lib/private/util.php b/lib/private/util.php
index 23c7053002c90201da920d9ff7649e9f4439a1d3..bf7f39ebb2058e0097a62395b0da740859a6475c 100755
--- a/lib/private/util.php
+++ b/lib/private/util.php
@@ -57,7 +57,10 @@ class OC_Util {
 				// set up quota for home storages, even for other users
 				// which can happen when using sharing
 
-				if ($storage instanceof \OC\Files\Storage\Home) {
+				/**
+				 * @var \OC\Files\Storage\Storage $storage
+				 */
+				if ($storage->instanceOfStorage('\OC\Files\Storage\Home')) {
 					$user = $storage->getUser()->getUID();
 					$quota = OC_Util::getUserQuota($user);
 					if ($quota !== \OC\Files\SPACE_UNLIMITED) {