diff --git a/lib/private/Files/Config/UserMountCache.php b/lib/private/Files/Config/UserMountCache.php
index 6ec78e4d81..5829fdf512 100644
--- a/lib/private/Files/Config/UserMountCache.php
+++ b/lib/private/Files/Config/UserMountCache.php
@@ -193,7 +193,11 @@ class UserMountCache implements IUserMountCache {
 		if (is_null($user)) {
 			return null;
 		}
-		return new CachedMountInfo($user, (int)$row['storage_id'], (int)$row['root_id'], $row['mount_point'], $row['mount_id'], isset($row['path'])? $row['path']:'');
+		$mount_id = $row['mount_id'];
+		if (!is_null($mount_id)) {
+			$mount_id = (int) $mount_id;
+		}
+		return new CachedMountInfo($user, (int)$row['storage_id'], (int)$row['root_id'], $row['mount_point'], $mount_id, isset($row['path'])? $row['path']:'');
 	}
 
 	/**