diff --git a/lib/private/Calendar/Resource/Manager.php b/lib/private/Calendar/Resource/Manager.php
index 2d1746cb98..baa8117e85 100644
--- a/lib/private/Calendar/Resource/Manager.php
+++ b/lib/private/Calendar/Resource/Manager.php
@@ -28,7 +28,7 @@ use OCP\Calendar\Resource\IBackend;
 class Manager implements \OCP\Calendar\Resource\IManager {
 
 	/** @var IBackend[] holds all registered resource backends */
-	private $backends;
+	private $backends = [];
 
 	/**
 	 * Registers a resource backend
diff --git a/lib/private/Calendar/Room/Manager.php b/lib/private/Calendar/Room/Manager.php
index 9ddf1f1d7b..aef9f2ed32 100644
--- a/lib/private/Calendar/Room/Manager.php
+++ b/lib/private/Calendar/Room/Manager.php
@@ -28,7 +28,7 @@ use OCP\Calendar\Room\IBackend;
 class Manager implements \OCP\Calendar\Room\IManager {
 
 	/** @var IBackend[] holds all registered resource backends */
-	private $backends;
+	private $backends = [];
 
 	/**
 	 * Registers a resource backend