diff --git a/core/lib/Drupal/Core/Cache/CacheCollector.php b/core/lib/Drupal/Core/Cache/CacheCollector.php
index 912b60f943..c7410435a4 100644
--- a/core/lib/Drupal/Core/Cache/CacheCollector.php
+++ b/core/lib/Drupal/Core/Cache/CacheCollector.php
@@ -166,6 +166,13 @@ public function set($key, $value) {
     unset($this->keysToRemove[$key]);
     $this->invalidateCache();
 
+    // Log a message if maintenance mode has been set.
+    if ($key == 'system.maintenance_mode') {
+      $log_message = $value ?
+        t('Maintenance Mode enabled') : t('Maintenance Mode disabled');
+      \Drupal::logger('system')->notice($log_message);
+    }
+
   }
 
   /**