diff --git a/lib/files/filesystem.php b/lib/files/filesystem.php
index 02cce001b481a29109c6d68e826414b003f011da..7e0bcfd1a27b76ff6751713751366abd3d07827e 100644
--- a/lib/files/filesystem.php
+++ b/lib/files/filesystem.php
@@ -359,7 +359,9 @@ class Filesystem {
 	 * clear all mounts and storage backends
 	 */
 	public static function clearMounts() {
-		self::$mounts->clear();
+		if (self::$mounts) {
+			self::$mounts->clear();
+		}
 	}
 
 	/**