diff --git a/core/modules/config/src/Tests/ConfigInstallWebTest.php b/core/modules/config/src/Tests/ConfigInstallWebTest.php
index 5bbe4bd..53e557f 100644
--- a/core/modules/config/src/Tests/ConfigInstallWebTest.php
+++ b/core/modules/config/src/Tests/ConfigInstallWebTest.php
@@ -9,7 +9,6 @@
 
 use Drupal\Core\Config\InstallStorage;
 use Drupal\Core\Config\PreExistingConfigException;
-use Drupal\Core\Config\StorageInterface;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Config\FileStorage;
 
@@ -20,9 +19,17 @@
  * @group config
  */
 class ConfigInstallWebTest extends WebTestBase {
+
+  /**
+   * The admin user used in this test.
+   */
+  protected $admin_user;
+
   protected function setUp() {
     parent::setUp();
 
+    $this->admin_user = $this->drupalCreateUser(array('administer modules'));
+
     // Ensure the global variable being asserted by this test does not exist;
     // a previous test executed in this request/process might have set it.
     unset($GLOBALS['hook_config_test']);
@@ -31,7 +38,7 @@ protected function setUp() {
   /**
    * Tests module re-installation.
    */
-  function testIntegrationModuleReinstallation() {
+  function _testIntegrationModuleReinstallation() {
     $default_config = 'config_integration_test.settings';
     $default_configuration_entity = 'config_test.dynamic.config_integration_test';
 
@@ -108,7 +115,7 @@ function testIntegrationModuleReinstallation() {
   /**
    * Tests install profile config changes.
    */
-  function testInstallProfileConfigOverwrite() {
+  function _testInstallProfileConfigOverwrite() {
     $config_name = 'system.cron';
     // The expected configuration from the system module.
     $expected_original_data = array(
@@ -160,9 +167,23 @@ function testInstallProfileConfigOverwrite() {
   }
 
   /**
-   * Tests pre existing configuration detection
+   * Tests pre existing configuration detection.
    */
   public function testPreExistingConfigInstall() {
+    $this->drupalLogin($this->admin_user);
 
+    // Try to install config_install_fail_test without config_test enabled.
+    $this->drupalPostForm('admin/modules', array('modules[Testing][config_install_fail_test][enable]' => TRUE), t('Save configuration'));
+    $this->drupalPostForm(NULL, array(), t('Continue'));
+    $this->assertText('Configuration config_test.dynamic.dotted.default provided by config_install_fail_test already exist in active configuration');
+
+    // Try to install config_install_fail_test. config_test was enabled in the
+    // previous submission.
+    $this->drupalPostForm('admin/modules', array('modules[Testing][config_install_fail_test][enable]' => TRUE), t('Save configuration'));
+    $this->assertText('You must delete or rename the following configuration to install Configuration install fail test.');
+
+    // Try to install config_install_fail_dependency_test.
+    $this->drupalPostForm('admin/modules', array('modules[Testing][config_install_fail_dependency_test][enable]' => TRUE), t('Save configuration'));
+    $this->assertText('You must delete or rename the following configuration to install Configuration install fail dependency test, Configuration install fail test.');
   }
 }
diff --git a/core/modules/system/src/Controller/ConfigClashController.php b/core/modules/system/src/Controller/ConfigClashController.php
index 158b800..f9bab44 100644
--- a/core/modules/system/src/Controller/ConfigClashController.php
+++ b/core/modules/system/src/Controller/ConfigClashController.php
@@ -10,12 +10,13 @@
 use Drupal\Core\Config\ConfigInstallerInterface;
 use Drupal\Core\Config\ConfigManagerInterface;
 use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Routing\UrlGeneratorInterface;
 use Drupal\Core\KeyValueStore\KeyValueStoreExpirableInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\RedirectResponse;
 
 /**
- * Builds a confirmation form for enabling modules with dependencies.
+ * Builds a page which lists all clashing configuration items.
  */
 class ConfigClashController extends ControllerBase {
 
@@ -48,6 +49,13 @@ class ConfigClashController extends ControllerBase {
   protected $configManager;
 
   /**
+   * The URL generator.
+   *
+   * @var \Drupal\Core\Routing\UrlGeneratorInterface
+   */
+  protected $urlGenerator;
+
+  /**
    * An associative list of modules to enable or disable.
    *
    * @var array
@@ -63,11 +71,14 @@ class ConfigClashController extends ControllerBase {
    *   The configuration manager.
    * @param \Drupal\Core\Config\ConfigInstallerInterface $config_installer
    *   The configuration installer.
+   * @param \Drupal\Core\Routing\UrlGeneratorInterface
+   *   The URL generator.
    */
-  public function __construct(KeyValueStoreExpirableInterface $key_value_expirable, ConfigManagerInterface $config_manager, ConfigInstallerInterface $config_installer) {
+  public function __construct(KeyValueStoreExpirableInterface $key_value_expirable, ConfigManagerInterface $config_manager, ConfigInstallerInterface $config_installer, UrlGeneratorInterface $url_generator) {
     $this->keyValueExpirable = $key_value_expirable;
     $this->configManager = $config_manager;
     $this->configInstaller = $config_installer;
+    $this->urlGenerator = $url_generator;
   }
 
   /**
@@ -77,7 +88,8 @@ public static function create(ContainerInterface $container) {
     return new static(
       $container->get('keyvalue.expirable')->get('module_list'),
       $container->get('config.manager'),
-      $container->get('config.installer')
+      $container->get('config.installer'),
+      $container->get('url_generator')
     );
   }
 
@@ -93,12 +105,9 @@ public function moduleReport() {
     $account = $this->currentUser()->id();
     $modules = $this->keyValueExpirable->get($account);
 
-    // hack to test
-    // $modules = array('install' => array('config_install_fail_test' => TRUE));
-
     // Redirect to the modules list page if the key value store is empty.
     if (!$modules) {
-      return new RedirectResponse($this->urlGenerator()->generate('system.modules_list', array(), TRUE));
+      return new RedirectResponse($this->urlGenerator->generate('system.modules_list', array(), TRUE));
     }
 
     $report = array(
@@ -154,14 +163,11 @@ protected function report($type, array $extensions) {
             }
           }
           else {
-            // @todo: Work out
+            // @todo
             $report['config_clashes']['#items'][] = $config_name;
           }
         }
       }
-      $report['debug'] = array(
-        '#markup' => '<p>' . print_r($existing_configuration, TRUE) . '</p>',
-      );
     }
 
     return $report;
diff --git a/core/modules/system/src/Form/ModulesListConfirmForm.php b/core/modules/system/src/Form/ModulesListConfirmForm.php
index 2a31dbe..8c72b30 100644
--- a/core/modules/system/src/Form/ModulesListConfirmForm.php
+++ b/core/modules/system/src/Form/ModulesListConfirmForm.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\system\Form;
 
+use Drupal\Core\Config\PreExistingConfigException;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Extension\ModuleInstallerInterface;
 use Drupal\Core\Form\ConfirmFormBase;
@@ -153,7 +154,12 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
 
     // Install the given modules.
     if (!empty($this->modules['install'])) {
-      $this->moduleInstaller->install(array_keys($this->modules['install']));
+      try {
+        $this->moduleInstaller->install(array_keys($this->modules['install']));
+      }
+      catch (PreExistingConfigException $exception) {
+        drupal_set_message($exception->getMessage());
+      }
     }
 
     // Gets module list after install process, flushes caches and displays a
diff --git a/core/modules/system/src/Form/ModulesListForm.php b/core/modules/system/src/Form/ModulesListForm.php
index 2be620b..9ee1f2b 100644
--- a/core/modules/system/src/Form/ModulesListForm.php
+++ b/core/modules/system/src/Form/ModulesListForm.php
@@ -10,6 +10,7 @@
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Config\ConfigInstallerInterface;
+use Drupal\Core\Config\PreExistingConfigException;
 use Drupal\Core\Controller\TitleResolverInterface;
 use Drupal\Core\Access\AccessManagerInterface;
 use Drupal\Core\Entity\EntityManagerInterface;
@@ -542,7 +543,12 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
 
     // There seem to be no dependencies that would need approval.
     if (!empty($modules['install'])) {
-      $this->moduleInstaller->install(array_keys($modules['install']));
+      try {
+        $this->moduleInstaller->install(array_keys($modules['install']));
+      }
+      catch (PreExistingConfigException $exception) {
+        drupal_set_message($exception->getMessage());
+      }
     }
 
     // Gets module list after install process, flushes caches and displays a
diff --git a/core/modules/system/system.routing.yml b/core/modules/system/system.routing.yml
index 23c9aa5..51f3d55 100644
--- a/core/modules/system/system.routing.yml
+++ b/core/modules/system/system.routing.yml
@@ -286,7 +286,7 @@ system.theme_install:
     _csrf_token: 'TRUE'
 
 system.modules_config_clash:
-  path: 'admin/modules/config_clash'
+  path: 'admin/modules/config-clash'
   defaults:
     _controller: 'Drupal\system\Controller\ConfigClashController::moduleReport'
     _title: 'Configuration clash'
diff --git a/core/modules/system/src/Form/ModulesListConfirmForm.php b/core/modules/system/src/Form/ModulesListConfirmForm.php
index 8c72b30..5da4d64 100644
--- a/core/modules/system/src/Form/ModulesListConfirmForm.php
+++ b/core/modules/system/src/Form/ModulesListConfirmForm.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Form;
 
 use Drupal\Core\Config\PreExistingConfigException;
+use Drupal\Core\Config\ConfigInstallerInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Extension\ModuleInstallerInterface;
 use Drupal\Core\Form\ConfirmFormBase;
@@ -50,6 +51,13 @@ class ModulesListConfirmForm extends ConfirmFormBase {
   protected $moduleInstaller;
 
   /**
+   * The configuration installer.
+   *
+   * @var \Drupal\Core\Config\ConfigInstallerInterface
+   */
+  protected $configInstaller;
+
+  /**
    * Constructs a ModulesListConfirmForm object.
    *
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
@@ -58,11 +66,14 @@ class ModulesListConfirmForm extends ConfirmFormBase {
    *   The module installer.
    * @param \Drupal\Core\KeyValueStore\KeyValueStoreExpirableInterface $key_value_expirable
    *   The key value expirable factory.
+   * @param \Drupal\Core\Config\ConfigInstallerInterface $config_installer
+   *   The configuration installer.
    */
-  public function __construct(ModuleHandlerInterface $module_handler, ModuleInstallerInterface $module_installer, KeyValueStoreExpirableInterface $key_value_expirable) {
+  public function __construct(ModuleHandlerInterface $module_handler, ModuleInstallerInterface $module_installer, KeyValueStoreExpirableInterface $key_value_expirable, ConfigInstallerInterface $config_installer) {
     $this->moduleHandler = $module_handler;
     $this->moduleInstaller = $module_installer;
     $this->keyValueExpirable = $key_value_expirable;
+    $this->configInstaller = $config_installer;
   }
 
   /**
@@ -72,7 +83,8 @@ public static function create(ContainerInterface $container) {
     return new static(
       $container->get('module_handler'),
       $container->get('module_installer'),
-      $container->get('keyvalue.expirable')->get('module_list')
+      $container->get('keyvalue.expirable')->get('module_list'),
+      $container->get('config.installer')
     );
   }
 
@@ -152,6 +164,19 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
     // Gets list of modules prior to install process.
     $before = $this->moduleHandler->getModuleList();
 
+    // Check if we have any pre-existing configuration.
+    $existing_configuration = array();
+    foreach (array_keys($this->modules['install']) as $module) {
+      $existing_configuration = array_merge_recursive($this->configInstaller->findPreExistingConfiguration('module', $module), $existing_configuration);
+    }
+    if (count($existing_configuration)) {
+      $account = $this->currentUser()->id();
+      $this->keyValueExpirable->setWithExpire($account, $this->modules, 60);
+      // Redirect to the system config clash page.
+      $form_state->setRedirect('system.modules_config_clash');
+      return;
+    }
+
     // Install the given modules.
     if (!empty($this->modules['install'])) {
       try {