diff --git a/core/modules/system/src/Controller/DbUpdateController.php b/core/modules/system/src/Controller/DbUpdateController.php
index 56c0bc0..c2e195e 100644
--- a/core/modules/system/src/Controller/DbUpdateController.php
+++ b/core/modules/system/src/Controller/DbUpdateController.php
@@ -545,11 +545,11 @@ protected function updateTasksList($active = NULL) {
    */
   protected function triggerBatch(Request $request) {
     $maintenance_mode = $this->state->get('system.maintenance_mode', FALSE);
-    // Store the prior value in the session so it can be restored at the end
-    // of the batch.
+    // Store the current maintenance mode status in the session so that it can
+    // be restored at the end of the batch.
     $_SESSION['maintenance_mode'] = $maintenance_mode;
-    // During the update, always bring the site offline so that schema changes
-    // do not affect visiting users.
+    // During the update, always put the site into maintenance mode so that
+    // in-progress schema changes do not affect visiting users.
     if (empty($maintenance_mode)) {
       $this->state->set('system.maintenance_mode', TRUE);
     }
diff --git a/core/modules/system/src/Tests/System/SiteMaintenanceTest.php b/core/modules/system/src/Tests/System/SiteMaintenanceTest.php
index 43c8d69..54ab8b7 100644
--- a/core/modules/system/src/Tests/System/SiteMaintenanceTest.php
+++ b/core/modules/system/src/Tests/System/SiteMaintenanceTest.php
@@ -45,7 +45,7 @@ protected function setUp() {
    */
   protected function testSiteMaintenance() {
     $this->drupalGet(Url::fromRoute('user.page'));
-    // JS Should be aggregated, so drupal.js is not in the page source.
+    // JS should be aggregated, so drupal.js is not in the page source.
     $links = $this->xpath('//script[contains(@src, :href)]', array(':href' => '/core/misc/drupal.js'));
     $this->assertFalse(isset($links[0]), 'script /core/misc/drupal.js not in page');
     // Turn on maintenance mode.
@@ -59,7 +59,7 @@ protected function testSiteMaintenance() {
     $offline_message = t('@site is currently under maintenance. We should be back shortly. Thank you for your patience.', array('@site' => $this->config('system.site')->get('name')));
 
     $this->drupalGet(Url::fromRoute('user.page'));
-    // JS Should not be aggregated, so drupal.js is in the page source.
+    // JS should not be aggregated, so drupal.js is expected in the page source.
     $links = $this->xpath('//script[contains(@src, :href)]', array(':href' => '/core/misc/drupal.js'));
     $this->assertTrue(isset($links[0]), 'script /core/misc/drupal.js in page');
     $this->assertRaw($admin_message, 'Found the site maintenance mode message.');
diff --git a/core/modules/system/src/Tests/Update/UpdateScriptTest.php b/core/modules/system/src/Tests/Update/UpdateScriptTest.php
index 589cd2d..d3e9d5e 100644
--- a/core/modules/system/src/Tests/Update/UpdateScriptTest.php
+++ b/core/modules/system/src/Tests/Update/UpdateScriptTest.php
@@ -202,6 +202,7 @@ function testSuccessfulUpdateFunctionality() {
     $this->clickLink('Administration pages');
     $this->assertResponse(200);
   }
+
   /**
    * Tests update.php while in maintenance mode.
    */