core/modules/block/src/Tests/BlockSystemBrandingTest.php     | 11 +++++++++++
 core/modules/system/src/Plugin/Block/SystemBrandingBlock.php | 11 ++++++-----
 core/modules/user/src/Form/UserPasswordResetForm.php         |  2 +-
 core/modules/user/src/Tests/UserLoginTest.php                |  2 ++
 4 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/core/modules/block/src/Tests/BlockSystemBrandingTest.php b/core/modules/block/src/Tests/BlockSystemBrandingTest.php
index 82cff41..448a1ca 100644
--- a/core/modules/block/src/Tests/BlockSystemBrandingTest.php
+++ b/core/modules/block/src/Tests/BlockSystemBrandingTest.php
@@ -38,6 +38,12 @@ protected function setUp() {
    * Tests system branding block configuration.
    */
   public function testSystemBrandingSettings() {
+    $assert_cache_tags = function() {
+      $cache_tags = explode(' ', $this->drupalGetHeader('X-Drupal-Cache-Tags'));
+      $this->assertTrue(in_array('config:system.site', $cache_tags));
+      $this->assertTrue(in_array('theme_global_setting', $cache_tags));
+    };
+
     $site_logo_xpath = '//div[@id="block-site-branding"]//a[@class="site-logo"]';
     $site_name_xpath = '//div[@id="block-site-branding"]//div[@class="site-name"]';
     $site_slogan_xpath = '//div[@id="block-site-branding"]//div[@class="site-slogan"]';
@@ -51,6 +57,7 @@ public function testSystemBrandingSettings() {
     $this->assertTrue(!empty($site_logo_element), 'The branding block logo was found.');
     $this->assertTrue(!empty($site_name_element), 'The branding block site name was found.');
     $this->assertTrue(!empty($site_slogan_element), 'The branding block slogan was found.');
+    $assert_cache_tags();
 
     // Turn just the logo off.
     $this->config('block.block.site-branding')
@@ -64,6 +71,7 @@ public function testSystemBrandingSettings() {
     $this->assertTrue(empty($site_logo_element), 'The branding block logo was disabled.');
     $this->assertTrue(!empty($site_name_element), 'The branding block site name was found.');
     $this->assertTrue(!empty($site_slogan_element), 'The branding block slogan was found.');
+    $assert_cache_tags();
 
     // Turn just the site name off.
     $this->config('block.block.site-branding')
@@ -78,6 +86,7 @@ public function testSystemBrandingSettings() {
     $this->assertTrue(!empty($site_logo_element), 'The branding block logo was found.');
     $this->assertTrue(empty($site_name_element), 'The branding block site name was disabled.');
     $this->assertTrue(!empty($site_slogan_element), 'The branding block slogan was found.');
+    $assert_cache_tags();
 
     // Turn just the site slogan off.
     $this->config('block.block.site-branding')
@@ -92,6 +101,7 @@ public function testSystemBrandingSettings() {
     $this->assertTrue(!empty($site_logo_element), 'The branding block logo was found.');
     $this->assertTrue(!empty($site_name_element), 'The branding block site name was found.');
     $this->assertTrue(empty($site_slogan_element), 'The branding block slogan was disabled.');
+    $assert_cache_tags();
 
     // Turn the site name and the site slogan off.
     $this->config('block.block.site-branding')
@@ -106,6 +116,7 @@ public function testSystemBrandingSettings() {
     $this->assertTrue(!empty($site_logo_element), 'The branding block logo was found.');
     $this->assertTrue(empty($site_name_element), 'The branding block site name was disabled.');
     $this->assertTrue(empty($site_slogan_element), 'The branding block slogan was disabled.');
+    $assert_cache_tags();
   }
 
 }
diff --git a/core/modules/system/src/Plugin/Block/SystemBrandingBlock.php b/core/modules/system/src/Plugin/Block/SystemBrandingBlock.php
index 1d99bb3..7dd5c54 100644
--- a/core/modules/system/src/Plugin/Block/SystemBrandingBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemBrandingBlock.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Plugin\Block;
 
 use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Cache\Cache;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
@@ -189,11 +190,11 @@ public function build() {
    * {@inheritdoc}
    */
   public function getCacheTags() {
-    // The theme-specific cache tag is set automatically for each block, but the
-    // output of this block also depends on the global theme settings.
-    $cache_tags = parent::getCacheTags();
-    $cache_tags[] = 'theme_global_setting';
-    return $cache_tags;
+    return Cache::mergeTags(
+      parent::getCacheTags(),
+      ['theme_global_setting'],
+      $this->configFactory->get('system.site')->getCacheTags()
+    );
   }
 
 }
diff --git a/core/modules/user/src/Form/UserPasswordResetForm.php b/core/modules/user/src/Form/UserPasswordResetForm.php
index 490965a..69b4588 100644
--- a/core/modules/user/src/Form/UserPasswordResetForm.php
+++ b/core/modules/user/src/Form/UserPasswordResetForm.php
@@ -97,7 +97,7 @@ public function buildForm(array $form, FormStateInterface $form_state, AccountIn
   }
 
   /**
-   * {@inheritdoc}o
+   * {@inheritdoc}
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
     /** @var $user \Drupal\user\UserInterface */
diff --git a/core/modules/user/src/Tests/UserLoginTest.php b/core/modules/user/src/Tests/UserLoginTest.php
index 1ffdddc..6f85658 100644
--- a/core/modules/user/src/Tests/UserLoginTest.php
+++ b/core/modules/user/src/Tests/UserLoginTest.php
@@ -23,6 +23,8 @@ class UserLoginTest extends WebTestBase {
   function testCacheTags() {
     $this->drupalGet('user/login');
     $cache_tags = explode(' ', $this->drupalGetHeader('X-Drupal-Cache-Tags'));
+    // The user login form says "Enter your <site name> username.", hence it
+    // depends on config:system.site, and its cache tags should be present.
     $this->assertTrue(in_array('config:system.site', $cache_tags));
   }