diff --git a/src/Control/Middleware/FlushMiddleware.php b/src/Control/Middleware/FlushMiddleware.php
index 374063eec36..c14fd319df6 100644
--- a/src/Control/Middleware/FlushMiddleware.php
+++ b/src/Control/Middleware/FlushMiddleware.php
@@ -3,17 +3,23 @@
 namespace SilverStripe\Control\Middleware;
 
 use SilverStripe\Control\HTTPRequest;
-use SilverStripe\Core\BaseKernel;
 use SilverStripe\Core\ClassInfo;
 use SilverStripe\Core\Flushable;
 use SilverStripe\Core\Injector\Injector;
 use SilverStripe\Core\Kernel;
+use SilverStripe\Dev\Deprecation;
 
 /**
  * Triggers a call to flush() on all implementors of Flushable.
+ * @deprecated 5.4.0 Will be replaced with flushing inside the Kernel directly.
  */
 class FlushMiddleware implements HTTPMiddleware
 {
+    public function __construct()
+    {
+        Deprecation::noticeWithNoReplacment('5.4.0', 'Will be replaced with flushing inside the Kernel directly.');
+    }
+
     public function process(HTTPRequest $request, callable $delegate)
     {
         $kernel = Injector::inst()->get(Kernel::class);