diff --git a/src/Control/Middleware/FlushMiddleware.php b/src/Control/Middleware/FlushMiddleware.php
index 374063eec..64cd4279a 100644
--- a/src/Control/Middleware/FlushMiddleware.php
+++ b/src/Control/Middleware/FlushMiddleware.php
@@ -3,9 +3,6 @@
 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;
 
@@ -17,16 +14,10 @@ class FlushMiddleware implements HTTPMiddleware
     public function process(HTTPRequest $request, callable $delegate)
     {
         $kernel = Injector::inst()->get(Kernel::class);
-        if ((method_exists($kernel, 'isFlushed') && $kernel->isFlushed())) {
+        if ($kernel->isFlushed()) {
             // Disable cache when flushing
             HTTPCacheControlMiddleware::singleton()->disableCache(true);
-
-            foreach (ClassInfo::implementorsOf(Flushable::class) as $class) {
-                /** @var Flushable|string $class */
-                $class::flush();
-            }
         }
-
         return $delegate($request);
     }
 }
diff --git a/src/Core/CoreKernel.php b/src/Core/CoreKernel.php
index ca9946f68..5626fd080 100644
--- a/src/Core/CoreKernel.php
+++ b/src/Core/CoreKernel.php
@@ -52,6 +52,14 @@ class CoreKernel extends BaseKernel
         $this->validateDatabase();
 
         $this->setBooted(true);
+
+        // Flush everything else that can be flushed, now that we're booted.
+        if ($flush) {
+            foreach (ClassInfo::implementorsOf(Flushable::class) as $class) {
+                /** @var Flushable|string $class */
+                $class::flush();
+            }
+        }
     }
 
     /**
diff --git a/tests/php/Control/FlushMiddlewareTest.php b/tests/php/Control/FlushMiddlewareTest.php
deleted file mode 100644
index a553d14ba..000000000
--- a/tests/php/Control/FlushMiddlewareTest.php
+++ /dev/null
@@ -1,26 +0,0 @@
-<?php
-
-namespace SilverStripe\Control\Tests;
-
-use SilverStripe\Core\Injector\Injector;
-use SilverStripe\Core\Kernel;
-use SilverStripe\Control\Tests\FlushMiddlewareTest\TestFlushable;
-use SilverStripe\Dev\FunctionalTest;
-
-class FlushMiddlewareTest extends FunctionalTest
-{
-    /**
-     * Assert that classes that implement flushable are called
-     */
-    public function testImplementorsAreCalled()
-    {
-        TestFlushable::$flushed = false;
-
-        Injector::inst()->get(Kernel::class)->boot(true);
-        $this->get('/');
-        $this->assertTrue(TestFlushable::$flushed);
-
-        // reset the kernel Flush flag
-        Injector::inst()->get(Kernel::class)->boot();
-    }
-}
diff --git a/tests/php/Core/KernelTest.php b/tests/php/Core/KernelTest.php
index c779f3495..afb5b37a7 100644
--- a/tests/php/Core/KernelTest.php
+++ b/tests/php/Core/KernelTest.php
@@ -15,6 +15,7 @@ use SilverStripe\Core\Environment;
 use ReflectionClass;
 use SilverStripe\ORM\DB;
 use ReflectionObject;
+use SilverStripe\Core\Tests\KernelTest\TestFlushable;
 
 class KernelTest extends SapphireTest
 {
@@ -85,7 +86,7 @@ class KernelTest extends SapphireTest
 
         $kernel->getConfigLoader()->getManifest();
     }
-    
+
     public function testReplicaDatabaseVarsLoaded()
     {
         // Set environment variables for a fake replica database
@@ -113,4 +114,16 @@ class KernelTest extends SapphireTest
             'password' => 'hi_people',
         ], $configs['replica_01']);
     }
+
+    public function testImplementorsAreCalled()
+    {
+        TestFlushable::$flushed = false;
+
+        $kernel = Injector::inst()->get(Kernel::class);
+        $kernel->boot(true);
+        $this->assertTrue(TestFlushable::$flushed);
+
+        // reset the kernel Flush flag
+        $kernel->boot();
+    }
 }
diff --git a/tests/php/Control/FlushMiddlewareTest/TestFlushable.php b/tests/php/Core/KernelTest/TestFlushable.php
similarity index 81%
rename from tests/php/Control/FlushMiddlewareTest/TestFlushable.php
rename to tests/php/Core/KernelTest/TestFlushable.php
index f1c290e16..8b1f2d87a 100644
--- a/tests/php/Control/FlushMiddlewareTest/TestFlushable.php
+++ b/tests/php/Core/KernelTest/TestFlushable.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace SilverStripe\Control\Tests\FlushMiddlewareTest;
+namespace SilverStripe\Core\Tests\KernelTest;
 
 use SilverStripe\Core\Flushable;
 use SilverStripe\Dev\TestOnly;