diff -u b/core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php b/core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php
--- b/core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php
+++ b/core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php
@@ -42,7 +42,11 @@
    * {@inheritdoc}
    */
   public function process(ContainerBuilder $container) {
-    $default_backend = $container->hasParameter('default_backend') ? $container->getParameter('default_backend') : 'mysql';
+    $default_backend = $container->hasParameter('default_backend') ? $container->getParameter('default_backend') : NULL;
+    // No default backend was configured, so continue as normal.
+    if (!isset($default_backend)) {
+      return;
+    }
 
     foreach ($container->findTaggedServiceIds('backend_overridable') as $id => $attributes) {
       // If the service is already an alias it is not the original backend, so
@@ -53,8 +57,7 @@
-      if ($container->hasDefinition("$default_backend.$id")) {
-        $container->setDefinition($id, new Alias("$default_backend.$id"));
+      if ($container->hasDefinition("$default_backend.$id") || $container->hasAlias("$default_backend.$id")) {
+        $container->setAlias($id, new Alias("$default_backend.$id"));
       }
     }
   }
 
 }
-
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Installer\Form;
 
+use Drupal\Component\Serialization\Yaml;
 use Drupal\Component\Utility\Crypt;
 use Drupal\Core\Database\Database;
 use Drupal\Core\Form\FormBase;
@@ -156,6 +157,12 @@ public function submitForm(array &$form, array &$form_state) {
 
     drupal_rewrite_settings($settings);
 
+    $conf_path = './' . conf_path(FALSE);
+    $services_file = $conf_path . '/services.yml';
+    // @TODO Should we put some logic in here to ensure that the file is read
+    //   and writable?
+    file_put_contents($services_file, Yaml::encode(array('parameters' => array('default_backend' => $database['driver']))));
+
     // Add the config directories to settings.php.
     drupal_install_config_directories();
 
only in patch2:
unchanged:
--- a/core/modules/system/src/Tests/Installer/InstallerTest.php
+++ b/core/modules/system/src/Tests/Installer/InstallerTest.php
@@ -30,6 +30,9 @@ public function testInstaller() {
     $this->assertRaw(t('Congratulations, you installed @drupal!', array(
       '@drupal' => drupal_install_profile_distribution_name(),
     )));
+
+    // Ensures that the services YML file got written and read.
+    $this->assertEqual(\Drupal::getContainer()->getParameter('default_backend'), \Drupal::database()->driver());
   }
 
 }
only in patch2:
unchanged:
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/BackendCompilerPassTest.php
@@ -0,0 +1,93 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Core\DependencyInjection\Compiler\BackendCompilerPassTest.
+ */
+
+namespace Drupal\Tests\Core\DependencyInjection\Compiler;
+
+use Drupal\Core\DependencyInjection\Compiler\BackendCompilerPass;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\DependencyInjection\Alias;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Definition;
+
+/**
+ * @coversDefaultClass \Drupal\Core\DependencyInjection\Compiler\BackendCompilerPass
+ * @group DependencyInjection
+ */
+class BackendCompilerPassTest extends UnitTestCase {
+
+  /**
+   * The tested backend compiler pass.
+   *
+   * @var \Drupal\Core\DependencyInjection\Compiler\BackendCompilerPass
+   */
+  protected $backendPass;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    $this->backendPass = new BackendCompilerPass();
+  }
+
+  /**
+   * Tests the process method.
+   *
+   * @param string $expected_class
+   *   The expected used class.
+   * @param \Symfony\Component\DependencyInjection\ContainerBuilder $container
+   *   The container.
+   *
+   * @dataProvider providerTestProcess
+   *
+   * @covers ::process
+   */
+  public function testProcess($expected_class, ContainerBuilder $container) {
+    $this->backendPass->process($container);
+
+    $this->assertInstanceOf($expected_class, $container->get('service'));
+  }
+
+  /**
+   * Provides test data for testProcess().
+   *
+   * @return array
+   */
+  public function providerTestProcess() {
+    $data = array();
+    // Add a container with no set default_backend.
+    $container = new ContainerBuilder();
+    $prefix = '\\' . __NAMESPACE__ . '\\';
+    $container->setDefinition('service', (new Definition($prefix . 'ServiceClassDefault'))->addTag('backend_overridable'));
+    $container->setDefinition('mysql.service', new Definition($prefix . 'ServiceClassMysql'));
+
+    $data[] = array($prefix . 'ServiceClassDefault', $container);
+
+    // Set the default_backend so the mysql service should be used.
+    $container = clone $container;
+    $container->setParameter('default_backend', 'mysql');
+    $data[] = array($prefix . 'ServiceClassMysql', $container);
+
+    // Configure a manual alias for the service, so ensure that it is not
+    // overridden by the default backend.
+    $container = clone $container;
+    $container->setDefinition('mariadb.service', new Definition($prefix . 'ServiceClassMariaDb'));
+    $container->setAlias('service', new Alias('mariadb.service'));
+    $data[] = array($prefix . 'ServiceClassMariaDb', $container);
+
+    return $data;
+  }
+
+}
+
+class ServiceClassDefault {
+}
+
+class ServiceClassMysql extends ServiceClassDefault {
+}
+
+class ServiceClassMariaDb extends ServiceClassMysql {
+}