diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 9f46bb4129..9ec13c72c8 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -502,6 +502,8 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE)
  * @deprecated in Drupal 8.5.0, will be removed before Drupal 9.0.0.
  *   Use \Drupal::service('messenger')->getMessages() or
  *   \Drupal::service('messenger')->getMessagesByType() instead.
+ *
+ * @see https://www.drupal.org/node/2774931
  */
 function drupal_get_messages($type = NULL, $clear_queue = TRUE) {
   /** @var \Drupal\Core\Messenger\MessengerInterface $messenger */
diff --git a/core/lib/Drupal/Core/Messenger/LegacyMessenger.php b/core/lib/Drupal/Core/Messenger/LegacyMessenger.php
index 50a51e6b9e..722dfae1c2 100644
--- a/core/lib/Drupal/Core/Messenger/LegacyMessenger.php
+++ b/core/lib/Drupal/Core/Messenger/LegacyMessenger.php
@@ -118,7 +118,7 @@ public function deleteByType($type) {
    *   @endcode
    *   If there are no messages set, the function returns NULL.
    *
-   * @internal 
+   * @internal
    */
   private function setMessage($message = NULL, $type = 'status', $repeat = FALSE) {
     if (isset($message)) {
@@ -138,7 +138,11 @@ private function setMessage($message = NULL, $type = 'status', $repeat = FALSE)
       }
 
       // Mark this page as being uncacheable.
-      \Drupal::service('page_cache_kill_switch')->trigger();
+      // This function might be called early on in the installer, so we check
+      // whether the service exists.
+      if (\Drupal::hasService('page_cache_kill_switch')) {
+        \Drupal::service('page_cache_kill_switch')->trigger();
+      }
     }
 
     // Messages not set when DB connection fails.