diff --git a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
index f4bd493ca4f6..c24fd28ef429 100644
--- a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
@@ -158,10 +158,13 @@ class SiteConfigureForm extends ConfigFormBase {
       '#weight' => -20,
       '#access' => empty($install_state['config_install_path']),
     ];
+    // 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' => $this->t("Automated emails, such as registration information, will be sent from this address. Use an address ending in your site's domain to help prevent these emails from being flagged as spam."),
       '#required' => TRUE,
       '#weight' => -15,
@@ -207,11 +210,14 @@ class SiteConfigureForm extends ConfigFormBase {
       '#weight' => 0,
       '#access' => empty($install_state['config_install_path']),
     ];
+    // 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(NULL, TRUE),
       '#weight' => 5,
       '#attributes' => ['class' => ['timezone-detect']],
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 000000000000..31a390557e08
--- /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 000000000000..0f718d0b8f49
--- /dev/null
+++ b/core/profiles/testing_site_config/testing_site_config.install
@@ -0,0 +1,22 @@
+<?php
+
+/**
+ * @file
+ * Install functions for the testing_site_config module.
+ */
+
+/**
+ * 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 (which is
+  // Australia/Sydney in the testing environment).
+  \Drupal::configFactory()->getEditable('system.date')
+    ->set('timezone.default', 'America/Los_Angeles')
+    ->save(TRUE);
+}
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerSiteConfigProfileTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerSiteConfigProfileTest.php
new file mode 100644
index 000000000000..791befd0468b
--- /dev/null
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerSiteConfigProfileTest.php
@@ -0,0 +1,63 @@
+<?php
+
+namespace Drupal\FunctionalTests\Installer;
+
+/**
+ * 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 {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $profile = 'testing_site_config';
+
+  /**
+   * The site mail we expect to be set from the install profile.
+   *
+   * @see testing_site_config_install()
+   */
+  const EXPECTED_SITE_MAIL = 'profile-testing-site-config@example.com';
+
+  /**
+   * The timezone we expect to be set from the install profile.
+   *
+   * @see testing_site_config_install()
+   */
+  const EXPECTED_TIMEZONE = 'America/Los_Angeles';
+
+  /**
+   * {@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', self::EXPECTED_SITE_MAIL);
+    $this->assertFieldByName('date_default_timezone', self::EXPECTED_TIMEZONE);
+
+    return parent::setUpSite();
+  }
+
+  /**
+   * Verify the correct site config was set.
+   */
+  public function testInstaller() {
+    $this->assertEqual($this->config('system.site')->get('mail'), self::EXPECTED_SITE_MAIL);
+    $this->assertEqual($this->config('system.date')->get('timezone.default'), self::EXPECTED_TIMEZONE);
+  }
+
+}