diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index e12c160669..eacf24876b 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -360,6 +360,9 @@ private function bootKernel() {
 
     $this->container = $kernel->getContainer();
 
+    // Add session to request.
+    $request->setSession($this->container->get('session'));
+
     // Ensure database tasks have been run.
     require_once __DIR__ . '/../../../includes/install.inc';
     $connection = Database::getConnection();
diff --git a/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php b/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php
index a21ec29b98..c1c0527bee 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php
@@ -535,6 +535,7 @@ public function testFormCacheDeletionUncached() {
    */
   public function testExceededFileSize() {
     $request = new Request([FormBuilderInterface::AJAX_FORM_REQUEST => TRUE]);
+    $request->setSession($this->request->getSession());
     $request_stack = new RequestStack();
     $request_stack->push($request);
     $this->formBuilder = $this->getMockBuilder('\Drupal\Core\Form\FormBuilder')
@@ -557,6 +558,7 @@ public function testExceededFileSize() {
    */
   public function testGetPostAjaxRequest() {
     $request = new Request([FormBuilderInterface::AJAX_FORM_REQUEST => TRUE], ['form_id' => 'different_form_id']);
+    $request->setSession($this->request->getSession());
     $request->setMethod('POST');
     $this->requestStack->push($request);
 
diff --git a/core/tests/Drupal/Tests/Core/Form/FormTestBase.php b/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
index f0cb2f22d6..a3e31ac37d 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
@@ -174,6 +174,7 @@ protected function setUp() {
     $this->account = $this->createMock('Drupal\Core\Session\AccountInterface');
     $this->themeManager = $this->createMock('Drupal\Core\Theme\ThemeManagerInterface');
     $this->request = new Request();
+    $this->request->setSession($this->createmock('Symfony\Component\HttpFoundation\Session\SessionInterface'));
     $this->eventDispatcher = $this->createMock('Symfony\Component\EventDispatcher\EventDispatcherInterface');
     $this->requestStack = new RequestStack();
     $this->requestStack->push($this->request);