diff --git a/core/modules/system/src/Tests/Update/SiteLogoAltTitleAddedTest.php b/core/modules/system/src/Tests/Update/SiteLogoAltTitleAddedTest.php
new file mode 100644
index 0000000..fcd702b
--- /dev/null
+++ b/core/modules/system/src/Tests/Update/SiteLogoAltTitleAddedTest.php
@@ -0,0 +1,58 @@
+<?php
+
+namespace Drupal\system\Tests\Update;
+
+/**
+ * Tests that the Site's logo alt and title values are added to each enabled
+ * theme as well as to the global theme settings.
+ *
+ * @see https://www.drupal.org/node/2780293
+ *
+ * @group system
+ */
+class SiteLogoAltTitleAddedTest extends UpdatePathTestBase {
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface
+   */
+  protected $themeHandler;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setDatabaseDumpFiles() {
+    $this->databaseDumpFiles = [
+      __DIR__ . '/../../../../system/tests/fixtures/update/drupal-8.bare.standard.php.gz',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->themeHandler = $this->container->get('theme_handler');
+  }
+
+  /**
+   * Tests system_update_8302().
+   */
+  public function testSiteLogoAltTitleAdded() {
+    $this->runUpdates();
+    $this->themeHandler->refreshInfo();
+
+    // Check that the global theme settings have the expected values after the
+    // update.
+    $this->assertEqual($this->config('system.theme.global')->get('logo.alt'), 'Home');
+    $this->assertEqual($this->config('system.theme.global')->get('logo.title'), 'Home');
+
+    // Check that each enabled theme has the exepected valuesafter the update.
+    foreach ($this->themeHandler->listInfo() as $theme) {
+      $this->assertEqual($this->config($theme->getName() . '.settings')->get('logo.alt'), 'Home');
+      $this->assertEqual($this->config($theme->getName() . '.settings')->get('logo.title'), 'Home');
+    }
+  }
+
+}
diff --git a/core/themes/classy/templates/block/block--system-branding-block.html.twig b/core/themes/classy/templates/block/block--system-branding-block.html.twig
index 7c03c2f..d24baf9 100644
--- a/core/themes/classy/templates/block/block--system-branding-block.html.twig
+++ b/core/themes/classy/templates/block/block--system-branding-block.html.twig
@@ -11,6 +11,8 @@
  * - site_logo: Logo for site as defined in Appearance or theme settings.
  * - site_name: Name for site as defined in Site information settings.
  * - site_slogan: Slogan for site as defined in Site information settings.
+ * - site_logo_alt: The alt attribute text for the site logo.
+ * - site_logo_title: The title attribute text for the site logo.
  */
 #}
 {% block content %}
diff --git a/core/themes/stable/templates/block/block--system-branding-block.html.twig b/core/themes/stable/templates/block/block--system-branding-block.html.twig
index c2dc2b6..67e35c6 100644
--- a/core/themes/stable/templates/block/block--system-branding-block.html.twig
+++ b/core/themes/stable/templates/block/block--system-branding-block.html.twig
@@ -11,6 +11,8 @@
  * - site_logo: Logo for site as defined in Appearance or theme settings.
  * - site_name: Name for site as defined in Site information settings.
  * - site_slogan: Slogan for site as defined in Site information settings.
+ * - site_logo_alt: The alt attribute text for the site logo.
+ * - site_logo_title: The title attribute text for the site logo.
  */
 #}
 {% block content %}