diff --git a/apps/dav/lib/CardDAV/SyncService.php b/apps/dav/lib/CardDAV/SyncService.php
index 5bd92015ad..6f6fa0ba37 100644
--- a/apps/dav/lib/CardDAV/SyncService.php
+++ b/apps/dav/lib/CardDAV/SyncService.php
@@ -261,7 +261,7 @@ class SyncService {
 	/**
 	 * @param IUser $user
 	 */
-	public function updateUser($user) {
+	public function updateUser(IUser $user) {
 		$systemAddressBook = $this->getLocalSystemAddressBook();
 		$addressBookId = $systemAddressBook['id'];
 		$converter = new Converter($this->accountManager);
diff --git a/apps/dav/lib/HookManager.php b/apps/dav/lib/HookManager.php
index b1bd039c65..27b6525be4 100644
--- a/apps/dav/lib/HookManager.php
+++ b/apps/dav/lib/HookManager.php
@@ -101,7 +101,9 @@ class HookManager {
 
 	public function postCreateUser($params) {
 		$user = $this->userManager->get($params['uid']);
-		$this->syncService->updateUser($user);
+		if ($user instanceof IUser) {
+			$this->syncService->updateUser($user);
+		}
 	}
 
 	public function preDeleteUser($params) {