diff --git a/lib/FakeUser.php b/lib/FakeUser.php
index cefef0713..3a920a0c2 100644
--- a/lib/FakeUser.php
+++ b/lib/FakeUser.php
@@ -80,7 +80,7 @@ public function getBackendClassName() {
 		throw new \RuntimeException('Not implemented');
 	}
 
-	public function getBackend() {
+	public function getBackend(): ?\OCP\UserInterface {
 		throw new \RuntimeException('Not implemented');
 	}