diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 0d72a1b..9e457ce 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -1221,6 +1221,11 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE)
  *   \Drupal::service('messenger')->getMessagesByType() instead.
  */
 function drupal_get_messages($type = NULL, $clear_queue = TRUE) {
+  // Workaround for Drush.
+  if (!\Drupal::hasService('messenger')) {
+    return array();
+  }
+
   /** @var \Drupal\Core\Messenger\MessengerInterface $messenger */
   $messenger = \Drupal::service('messenger');
 
diff --git a/core/tests/Drupal/Tests/Core/Messenger/MessengerTest.php b/core/tests/Drupal/Tests/Core/Messenger/MessengerTest.php
index af4b6cf..1a042bc 100644
--- a/core/tests/Drupal/Tests/Core/Messenger/MessengerTest.php
+++ b/core/tests/Drupal/Tests/Core/Messenger/MessengerTest.php
@@ -46,7 +46,7 @@ public static function getInfo() {
   public function setUp() {
     $this->messenger = new Messenger();
 
-    $this->existingSession = isset($_SESSION) ? $_SESSION : array();
+    $this->existingSession = isset($_SESSION) ? $_SESSION : NULL;
     $_SESSION = array();
   }
 
@@ -54,9 +54,12 @@ public function setUp() {
    * {@inheritdoc}
    */
   public function tearDown() {
-    if (!empty($this->existingSession)) {
+    if ($this->existingSession !== NULL) {
       $_SESSION = $this->existingSession;
     }
+    else {
+      unset($_SESSION);
+    }
   }
 
   /**