diff --git a/UPGRADE-4.3.md b/UPGRADE-4.3.md
index 20b970c15a..40d50e583f 100644
--- a/UPGRADE-4.3.md
+++ b/UPGRADE-4.3.md
@@ -57,6 +57,12 @@ EventDispatcher
  * The signature of the `EventDispatcherInterface::dispatch()` method should be updated to `dispatch($event, string $eventName = null)`, not doing so is deprecated
  * The `Event` class has been deprecated, use `Symfony\Contracts\EventDispatcher\Event` instead
 
+Filesystem
+----------
+
+ * Support for passing arrays to `Filesystem::dumpFile()` is deprecated.
+ * Support for passing arrays to `Filesystem::appendToFile()` is deprecated.
+
 Form
 ----