diff --git a/core/lib/Drupal/Core/Form/FormCache.php b/core/lib/Drupal/Core/Form/FormCache.php
index 3b7f706..92ab026 100644
--- a/core/lib/Drupal/Core/Form/FormCache.php
+++ b/core/lib/Drupal/Core/Form/FormCache.php
@@ -230,7 +230,6 @@ public function setCache($form_build_id, $form, FormStateInterface $form_state)
    */
   public function deleteCache($form_build_id) {
     $this->keyValueExpirableFactory->get('form')->delete($form_build_id);
-    $this->keyValueExpirableFactory->get('form_state')->delete($form_build_id);
     $session = $this->requestStack->getMasterRequest()->getSession();
     $session->remove('form_state:' . $form_build_id);
   }
diff --git a/core/modules/dblog/src/Tests/DbLogFormInjectionTest.php b/core/modules/dblog/src/Tests/DbLogFormInjectionTest.php
index e622fe2..81b9725 100644
--- a/core/modules/dblog/src/Tests/DbLogFormInjectionTest.php
+++ b/core/modules/dblog/src/Tests/DbLogFormInjectionTest.php
@@ -92,6 +92,9 @@ protected function setUp() {
     ));
     $test_user->save();
     \Drupal::service('current_user')->setAccount($test_user);
+    $session = \Drupal::service('session');
+    \Drupal::request()->setSession($session);
+    $session->start();
   }
 
   /**
diff --git a/core/modules/system/src/Tests/Form/FormCacheTest.php b/core/modules/system/src/Tests/Form/FormCacheTest.php
index 77d259e..7d5b86d 100644
--- a/core/modules/system/src/Tests/Form/FormCacheTest.php
+++ b/core/modules/system/src/Tests/Form/FormCacheTest.php
@@ -52,6 +52,9 @@ protected function setUp() {
     );
     $this->formState = new FormState();
     $this->formState->set('example', $this->randomMachineName());
+    $session = \Drupal::service('session');
+    \Drupal::request()->setSession($session);
+    $session->start();
   }
 
   /**
diff --git a/core/modules/system/src/Tests/Queue/QueueSerializationTest.php b/core/modules/system/src/Tests/Queue/QueueSerializationTest.php
index 9108ac2..56acbb5 100644
--- a/core/modules/system/src/Tests/Queue/QueueSerializationTest.php
+++ b/core/modules/system/src/Tests/Queue/QueueSerializationTest.php
@@ -90,6 +90,9 @@ protected function setUp() {
     ));
     $test_user->save();
     \Drupal::service('current_user')->setAccount($test_user);
+    $session = \Drupal::service('session');
+    \Drupal::request()->setSession($session);
+    $session->start();
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Form/FormCacheTest.php b/core/tests/Drupal/Tests/Core/Form/FormCacheTest.php
index 36f1146..cc31a7e 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormCacheTest.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormCacheTest.php
@@ -301,7 +301,7 @@ public function testLoadCachedFormState() {
     $this->session->expects($this->once())
       ->method('get')
       ->with('form_state:' . $form_build_id)
-      ->willReturn(['data' => $cached_form_state, 'expires' => $this->requestTime + 604800]);
+      ->willReturn(serialize(['data' => $cached_form_state, 'expires' => $this->requestTime + 604800]));
 
     $this->formCache->getCache($form_build_id, $form_state);
     $this->assertSame($cached_form_state['storage'], $form_state->getStorage());
@@ -346,7 +346,7 @@ public function testLoadCachedFormStateWithFiles() {
     $this->session->expects($this->once())
       ->method('get')
       ->with('form_state:' . $form_build_id)
-      ->willReturn(['data' => $cached_form_state, 'expires' => $this->requestTime + 604800]);
+      ->willReturn(serialize(['data' => $cached_form_state, 'expires' => $this->requestTime + 604800]));
 
     $this->formCache->getCache($form_build_id, $form_state);
   }
@@ -378,7 +378,7 @@ public function testLoadCachedFormStateWithSafeStrings() {
     $this->session->expects($this->once())
       ->method('get')
       ->with('form_state:' . $form_build_id)
-      ->willReturn(['data' => $cached_form_state, 'expires' => $this->requestTime + 604800]);
+      ->willReturn(serialize(['data' => $cached_form_state, 'expires' => $this->requestTime + 604800]));
 
     $this->formCache->getCache($form_build_id, $form_state);
   }
@@ -401,7 +401,7 @@ public function testSetCacheWithForm() {
     $form_state_data['build_info']['safe_strings'] = [];
     $this->session->expects($this->once())
       ->method('set')
-      ->with('form_state:' . $form_build_id, ['expires' => $this->requestTime + 21600, 'data' => $form_state_data]);
+      ->with('form_state:' . $form_build_id, serialize(['expires' => $this->requestTime + 21600, 'data' => $form_state_data]));
 
     $this->formCache->setCache($form_build_id, $form, $form_state);
   }
@@ -421,7 +421,7 @@ public function testSetCacheWithoutForm() {
     $form_state_data['build_info']['safe_strings'] = [];
     $this->session->expects($this->once())
       ->method('set')
-      ->with('form_state:' . $form_build_id, ['expires' => $this->requestTime + 21600, 'data' => $form_state_data]);
+      ->with('form_state:' . $form_build_id, serialize(['expires' => $this->requestTime + 21600, 'data' => $form_state_data]));
 
     $this->formCache->setCache($form_build_id, $form, $form_state);
   }
@@ -445,7 +445,7 @@ public function testSetCacheAuthUser() {
     $form_state_data['build_info']['safe_strings'] = [];
     $this->session->expects($this->once())
       ->method('set')
-      ->with('form_state:' . $form_build_id, ['expires' => $this->requestTime + 21600, 'data' => $form_state_data]);
+      ->with('form_state:' . $form_build_id, serialize(['expires' => $this->requestTime + 21600, 'data' => $form_state_data]));
 
     $this->csrfToken->expects($this->once())
       ->method('get')
@@ -478,7 +478,7 @@ public function testSetCacheWithSafeStrings() {
     ];
     $this->session->expects($this->once())
       ->method('set')
-      ->with('form_state:' . $form_build_id, ['expires' => $this->requestTime + 21600, 'data' => $form_state_data]);
+      ->with('form_state:' . $form_build_id, serialize(['expires' => $this->requestTime + 21600, 'data' => $form_state_data]));
 
     $this->formCache->setCache($form_build_id, $form, $form_state);
   }
@@ -514,9 +514,7 @@ public function testDeleteCache() {
     $this->formCacheStore->expects($this->once())
       ->method('delete')
       ->with($form_build_id);
-    $this->formStateCacheStore->expects($this->once())
-      ->method('delete')
-      ->with($form_build_id);
+
     $this->formCache->deleteCache($form_build_id);
   }