diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index a6e918f..32e23dd 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -725,6 +725,8 @@ function install_tasks($install_state) {
       'run' => $install_state['settings_verified'] ? INSTALL_TASK_SKIP : INSTALL_TASK_RUN_IF_NOT_COMPLETED,
       'function' => 'Drupal\Core\Installer\Form\SiteSettingsForm',
     ),
+    'install_write_profile' => array(
+    ),
     'install_verify_database_ready' => array(
       'run' => $install_state['database_ready'] ? INSTALL_TASK_SKIP : INSTALL_TASK_RUN_IF_NOT_COMPLETED,
     ),
@@ -1173,6 +1175,10 @@ function install_select_profile(&$install_state) {
  *   selected.
  */
 function _install_select_profile(&$install_state) {
+  // Use install profile from settings.php if it is set already.
+  if ($existing_profile = Settings::get('install_profile')) {
+    return $existing_profile;
+  }
   // Don't need to choose profile if only one available.
   if (count($install_state['profiles']) == 1) {
     return key($install_state['profiles']);
@@ -2258,3 +2264,20 @@ function install_display_requirements($install_state, $requirements) {
     }
   }
 }
+
+/**
+ * Installation task; ensures install profile is written to settings.php.
+ *
+ * @param $install_state
+ *   An array of information about the current installation state.
+ */
+function install_write_profile($install_state) {
+  if (Settings::get('install_profile') !== $install_state['parameters']['profile']) {
+    // Remember the profile which was used.
+    $settings['settings']['install_profile'] = (object) array(
+      'value' => $install_state['parameters']['profile'],
+      'required' => TRUE,
+    );
+    drupal_rewrite_settings($settings);
+  }
+}
diff --git a/core/modules/system/src/Tests/Installer/InstallerExistingSettingsNoProfileTest.php b/core/modules/system/src/Tests/Installer/InstallerExistingSettingsNoProfileTest.php
new file mode 100644
index 0000000..61dd5be
--- /dev/null
+++ b/core/modules/system/src/Tests/Installer/InstallerExistingSettingsNoProfileTest.php
@@ -0,0 +1,79 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Installer\InstallerExistingSettingsNoProfileTest.
+ */
+
+namespace Drupal\system\Tests\Installer;
+
+use Drupal\Core\Site\Settings;
+use Drupal\simpletest\InstallerTestBase;
+use Drupal\Core\Database\Database;
+
+/**
+ * Tests the installer with an existing settings file but no install profile.
+ *
+ * @group Installer
+ */
+class InstallerExistingSettingsNoProfileTest extends InstallerTestBase {
+
+  /**
+   * {@inheritdoc}
+   *
+   * Configures a preexisting settings.php file without an install_profile
+   * setting before invoking the interactive installer.
+   */
+  protected function setUp() {
+    // Pre-configure hash salt.
+    // Any string is valid, so simply use the class name of this test.
+    $this->settings['settings']['hash_salt'] = (object) array(
+      'value' => __CLASS__,
+      'required' => TRUE,
+    );
+
+    // Pre-configure database credentials.
+    $connection_info = Database::getConnectionInfo();
+    unset($connection_info['default']['pdo']);
+    unset($connection_info['default']['init_commands']);
+
+    $this->settings['databases']['default'] = (object) array(
+      'value' => $connection_info,
+      'required' => TRUE,
+    );
+
+    // Pre-configure config directories.
+    $this->settings['config_directories'] = array(
+      CONFIG_ACTIVE_DIRECTORY => (object) array(
+        'value' => conf_path() . '/files/config_active',
+        'required' => TRUE,
+      ),
+      CONFIG_STAGING_DIRECTORY => (object) array(
+        'value' => conf_path() . '/files/config_staging',
+        'required' => TRUE,
+      ),
+    );
+    mkdir($this->settings['config_directories'][CONFIG_ACTIVE_DIRECTORY]->value, 0777, TRUE);
+    mkdir($this->settings['config_directories'][CONFIG_STAGING_DIRECTORY]->value, 0777, TRUE);
+
+    parent::setUp();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUpSettings() {
+    // This step should not appear, since settings.php is fully configured
+    // already.
+  }
+
+  /**
+   * Verifies that installation succeeded.
+   */
+  public function testInstaller() {
+    $this->assertUrl('user/1');
+    $this->assertResponse(200);
+    $this->assertEqual('testing', Settings::get('install_profile'));
+  }
+
+}
diff --git a/core/modules/system/src/Tests/Installer/InstallerExistingSettingsTest.php b/core/modules/system/src/Tests/Installer/InstallerExistingSettingsTest.php
index 1951f57..3027d76 100644
--- a/core/modules/system/src/Tests/Installer/InstallerExistingSettingsTest.php
+++ b/core/modules/system/src/Tests/Installer/InstallerExistingSettingsTest.php
@@ -33,8 +33,6 @@ protected function setUp() {
 
     // Actually the install profile should be skipped to because it is written
     // to settings.php.
-    // @todo https://www.drupal.org/node/2451369 Fix install_profile so that it
-    //   is written to an existing settings.php if possible or if set used.
     $this->settings['settings']['install_profile'] = (object) array(
       'value' => 'testing',
       'required' => TRUE,
@@ -70,6 +68,14 @@ protected function setUp() {
   /**
    * {@inheritdoc}
    */
+  protected function setUpProfile() {
+    // This step should not appear, since settings.php is fully configured
+    // already.
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   protected function setUpSettings() {
     // This step should not appear, since settings.php is fully configured
     // already.