diff --git a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
index c28b7f8fd4..7ff231713e 100644
--- a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
@@ -152,10 +152,13 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#required' => TRUE,
       '#weight' => -20,
     ];
+    // Use the default site mail if one is already configured, or fall back to
+    // PHP's configured sendmail_from.
+    $default_site_mail = $this->config('system.site')->get('mail') ?: ini_get('sendmail_from');
     $form['site_information']['site_mail'] = [
       '#type' => 'email',
       '#title' => $this->t('Site email address'),
-      '#default_value' => ini_get('sendmail_from'),
+      '#default_value' => $default_site_mail,
       '#description' => $this->t("Automated emails, such as registration information, will be sent from this address. Use an address ending in your site's domain to help prevent these emails from being flagged as spam."),
       '#required' => TRUE,
       '#weight' => -15,
@@ -199,11 +202,14 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#description' => $this->t('Select the default country for the site.'),
       '#weight' => 0,
     ];
+    // Use the default site timezone if one is already configured, or fall back
+    // to the system timezone if set (and avoid throwing a warning in
+    // PHP >=5.4).
+    $default_timezone = $this->config('system.date')->get('timezone.default') ?: @date_default_timezone_get();
     $form['regional_settings']['date_default_timezone'] = [
       '#type' => 'select',
       '#title' => $this->t('Default time zone'),
-      // Use system timezone if set, but avoid throwing a warning in PHP >=5.4
-      '#default_value' => @date_default_timezone_get(),
+      '#default_value' => $default_timezone,
       '#options' => system_time_zones(),
       '#description' => $this->t('By default, dates in this site will be displayed in the chosen time zone.'),
       '#weight' => 5,
diff --git a/core/modules/system/src/Tests/Installer/InstallerSiteConfigDefaultTest.php b/core/modules/system/src/Tests/Installer/InstallerSiteConfigDefaultTest.php
new file mode 100644
index 0000000000..1117bea095
--- /dev/null
+++ b/core/modules/system/src/Tests/Installer/InstallerSiteConfigDefaultTest.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace Drupal\system\Tests\Installer;
+
+use Drupal\simpletest\InstallerTestBase;
+
+/**
+ * Verifies that the installer defaults to using the system email address and
+ * timezone.
+ *
+ * @group Installer
+ */
+class InstallerSiteConfigDefaultTest extends InstallerTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUpSite() {
+    $this->assertFieldByName('site_mail', ini_get('sendmail_from'));
+    $this->assertFieldByName('date_default_timezone', @date_default_timezone_get());
+
+    return parent::setUpSite();
+  }
+
+  /**
+   * Verify the correct site config was set.
+   */
+  public function testInstaller() {
+    $this->assertEqual(\Drupal::config('system.site')->get('mail'), $this->parameters['forms']['install_configure_form']['site_mail']);
+    $this->assertEqual(\Drupal::config('system.date')->get('timezone.default'), @date_default_timezone_get());
+  }
+
+}
diff --git a/core/modules/system/src/Tests/Installer/InstallerSiteConfigProfileTest.php b/core/modules/system/src/Tests/Installer/InstallerSiteConfigProfileTest.php
new file mode 100644
index 0000000000..421cb48936
--- /dev/null
+++ b/core/modules/system/src/Tests/Installer/InstallerSiteConfigProfileTest.php
@@ -0,0 +1,61 @@
+<?php
+
+namespace Drupal\system\Tests\Installer;
+
+use Drupal\simpletest\InstallerTestBase;
+
+/**
+ * Verifies that the installer defaults to the existing site email address and
+ * timezone, if they were provided by the install profile.
+ *
+ * @group Installer
+ */
+class InstallerSiteConfigProfileTest extends InstallerTestBase {
+
+  protected $profile = 'testing_site_config';
+  protected $profile_site_mail = 'profile-testing-site-config@example.com';
+  protected $profile_timezone;
+
+  public function __construct($test_id = NULL) {
+    parent::__construct($test_id);
+
+    // The install profile set the timezone to one of two possibilities, but
+    // never to the system timezone. (See testing_site_config.install.)
+    $this->profile_timezone = 'America/Los_Angeles';
+    if ($this->profile_timezone == @date_default_timezone_get()) {
+      $this->profile_timezone = 'America/New_York';
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function installParameters() {
+    $parameters = parent::installParameters();
+
+    // Don't override the site email address, allowing it to default to the one
+    // from our install profile.
+    unset($parameters['forms']['install_configure_form']['site_mail']);
+
+    return $parameters;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUpSite() {
+    $this->assertFieldByName('site_mail', $this->profile_site_mail);
+    $this->assertFieldByName('date_default_timezone', $this->profile_timezone);
+
+    return parent::setUpSite();
+  }
+
+  /**
+   * Verify the correct site config was set.
+   */
+  public function testInstaller() {
+    $this->assertEqual(\Drupal::config('system.site')->get('mail'), $this->profile_site_mail);
+    $this->assertEqual(\Drupal::config('system.date')->get('timezone.default'), $this->profile_timezone);
+  }
+
+}
diff --git a/core/profiles/testing_site_config/testing_site_config.info.yml b/core/profiles/testing_site_config/testing_site_config.info.yml
new file mode 100644
index 0000000000..31a390557e
--- /dev/null
+++ b/core/profiles/testing_site_config/testing_site_config.info.yml
@@ -0,0 +1,6 @@
+name: Testing site config
+type: profile
+description: 'Minimal profile for testing with default site config.'
+version: VERSION
+core: 8.x
+hidden: true
diff --git a/core/profiles/testing_site_config/testing_site_config.install b/core/profiles/testing_site_config/testing_site_config.install
new file mode 100644
index 0000000000..954e4a0b66
--- /dev/null
+++ b/core/profiles/testing_site_config/testing_site_config.install
@@ -0,0 +1,20 @@
+<?php
+
+/**
+ * Implements hook_install().
+ */
+function testing_site_config_install() {
+  // Set the site email address to something that is not sendmail_from.
+  \Drupal::configFactory()->getEditable('system.site')
+    ->set('mail', 'profile-testing-site-config@example.com')
+    ->save(TRUE);
+
+  // Set the time zone to something that is not the system timezone.
+  $timezone = 'America/Los_Angeles';
+  if ($timezone == @date_default_timezone_get()) {
+    $timezone = 'America/New_York';
+  }
+  \Drupal::configFactory()->getEditable('system.date')
+    ->set('timezone.default', $timezone)
+    ->save(TRUE);
+}