diff --git a/core/lib/Drupal.php b/core/lib/Drupal.php
index 141686f..1c48f4a 100644
--- a/core/lib/Drupal.php
+++ b/core/lib/Drupal.php
@@ -297,12 +297,14 @@ public static function lock() {
    *   The name of the configuration object to retrieve. The name corresponds to
    *   a configuration file. For @code \Drupal::config('book.admin') @endcode, the config
    *   object returned will contain the contents of book.admin configuration file.
+   * @param bool $mutable
+   *   (optional) Create an mutable configuration object. Defaults to TRUE.
    *
    * @return \Drupal\Core\Config\Config
    *   A configuration object.
    */
-  public static function config($name) {
-    return static::$container->get('config.factory')->get($name);
+  public static function config($name, $mutable = TRUE) {
+    return static::$container->get('config.factory')->get($name, $mutable);
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Config/ConfigFactory.php b/core/lib/Drupal/Core/Config/ConfigFactory.php
index 970a500..38df2d0 100644
--- a/core/lib/Drupal/Core/Config/ConfigFactory.php
+++ b/core/lib/Drupal/Core/Config/ConfigFactory.php
@@ -104,12 +104,12 @@ public function getOverrideState() {
   /**
    * {@inheritdoc}
    */
-  public function get($name) {
-    if ($config = $this->loadMultiple(array($name))) {
+  public function get($name, $mutable = TRUE) {
+    if ($config = $this->loadMultiple(array($name), $mutable)) {
       return $config[$name];
     }
     else {
-      $cache_key = $this->getConfigCacheKey($name);
+      $cache_key = $this->getConfigCacheKey($name, $mutable);
       // If the config object has been deleted it will already exist in the
       // cache but self::loadMultiple does not return such objects.
       // @todo Explore making ConfigFactory a listener to the config.delete
@@ -118,7 +118,7 @@ public function get($name) {
         // If the configuration object does not exist in the configuration
         // storage or static cache create a new object and add it to the static
         // cache.
-        $this->cache[$cache_key] = new Config($name, $this->storage, $this->eventDispatcher, $this->typedConfigManager);
+        $this->cache[$cache_key] = $this->createConfigObject($name, $mutable);
 
         if ($this->useOverrides) {
           // Get and apply any overrides.
@@ -139,13 +139,13 @@ public function get($name) {
   /**
    * {@inheritdoc}
    */
-  public function loadMultiple(array $names) {
+  public function loadMultiple(array $names, $mutable = TRUE) {
     $list = array();
 
     foreach ($names as $key => $name) {
       // @todo: Deleted configuration stays in $this->cache, only return
       //   configuration objects that are not new.
-      $cache_key = $this->getConfigCacheKey($name);
+      $cache_key = $this->getConfigCacheKey($name, $mutable);
       if (isset($this->cache[$cache_key]) && !$this->cache[$cache_key]->isNew()) {
         $list[$name] = $this->cache[$cache_key];
         unset($names[$key]);
@@ -164,9 +164,9 @@ public function loadMultiple(array $names) {
       }
 
       foreach ($storage_data as $name => $data) {
-        $cache_key = $this->getConfigCacheKey($name);
+        $cache_key = $this->getConfigCacheKey($name, $mutable);
 
-        $this->cache[$cache_key] = new Config($name, $this->storage, $this->eventDispatcher, $this->typedConfigManager);
+        $this->cache[$cache_key] = $this->createConfigObject($name, $mutable);
         $this->cache[$cache_key]->initWithData($data);
         if ($this->useOverrides) {
           if (isset($module_overrides[$name])) {
@@ -226,15 +226,15 @@ public function reset($name = NULL) {
   /**
    * {@inheritdoc}
    */
-  public function rename($old_name, $new_name) {
+  public function rename($old_name, $new_name, $mutable = TRUE) {
     $this->storage->rename($old_name, $new_name);
-    $old_cache_key = $this->getConfigCacheKey($old_name);
-    if (isset($this->cache[$old_cache_key])) {
+    $old_cache_keys = $this->getConfigCacheKeys($old_name);
+    foreach ($old_cache_keys as $old_cache_key) {
       unset($this->cache[$old_cache_key]);
     }
 
     // Prime the cache and load the configuration with the correct overrides.
-    $config = $this->get($new_name);
+    $config = $this->get($new_name, $mutable);
     $this->eventDispatcher->dispatch(ConfigEvents::RENAME, new ConfigRenameEvent($config, $old_name));
     return $config;
   }
@@ -260,12 +260,14 @@ public function getCacheKeys() {
    *
    * @param string $name
    *   The name of the configuration object.
+   * @param bool $mutable
+   *   Whether or not the object is mutable.
    *
    * @return string
    *   The cache key.
    */
-  protected function getConfigCacheKey($name) {
-    return $name . ':' . implode(':', $this->getCacheKeys());
+  protected function getConfigCacheKey($name, $mutable) {
+    return $name . ':' . implode(':', $this->getCacheKeys()) . ':' . ($mutable ? static::MUTABLE: static::IMMUTABLE);
   }
 
   /**
@@ -333,4 +335,22 @@ public function addOverride(ConfigFactoryOverrideInterface $config_factory_overr
     $this->configFactoryOverrides[] = $config_factory_override;
   }
 
+  /**
+   * Creates a configuration object.
+   *
+   * @param string $name
+   *   Configuration object name.
+   * @param bool $mutable
+   *   Determines whether a mutable or immutable config object is returned.
+   *
+   * @return \Drupal\Core\Config\Config|\Drupal\Core\Config\ImmutableConfig
+   *   The configuration object.
+   */
+  protected function createConfigObject($name, $mutable) {
+    if (!$mutable) {
+      return new ImmutableConfig($name, $this->storage, $this->eventDispatcher, $this->typedConfigManager);
+    }
+    return new Config($name, $this->storage, $this->eventDispatcher, $this->typedConfigManager);
+
+  }
 }
diff --git a/core/lib/Drupal/Core/Config/ConfigFactoryInterface.php b/core/lib/Drupal/Core/Config/ConfigFactoryInterface.php
index d51e023..751007b 100644
--- a/core/lib/Drupal/Core/Config/ConfigFactoryInterface.php
+++ b/core/lib/Drupal/Core/Config/ConfigFactoryInterface.php
@@ -15,6 +15,16 @@
 interface ConfigFactoryInterface {
 
   /**
+   * Constant used in static cache keys for mutable config objects.
+   */
+  const MUTABLE = 'mutable';
+
+  /**
+   * Constant used in static cache keys for immutable config objects.
+   */
+  const IMMUTABLE = 'immutable';
+
+  /**
    * Sets the override state.
    *
    * @param bool $state
@@ -37,11 +47,13 @@ public function getOverrideState();
    *
    * @param string $name
    *   The name of the configuration object to construct.
+   * @param bool $mutable
+   *   (optional) Create an mutable configuration object. Defaults to TRUE.
    *
-   * @return \Drupal\Core\Config\Config
+   * @return \Drupal\Core\Config\Config|\Drupal\Core\Config\ImmutableConfig
    *   A configuration object.
    */
-  public function get($name);
+  public function get($name, $mutable = TRUE);
 
   /**
    * Returns a list of configuration objects for the given names.
@@ -51,11 +63,13 @@ public function get($name);
    *
    * @param array $names
    *   List of names of configuration objects.
+   * @param bool $mutable
+   *   (optional) Create an mutable configuration object. Defaults to TRUE.
    *
-   * @return \Drupal\Core\Config\Config[]
+   * @return \Drupal\Core\Config\Config[]|\Drupal\Core\Config\ImmutableConfig[]
    *   List of successfully loaded configuration objects, keyed by name.
    */
-  public function loadMultiple(array $names);
+  public function loadMultiple(array $names, $mutable = TRUE);
 
   /**
    * Resets and re-initializes configuration objects. Internal use only.
@@ -75,11 +89,13 @@ public function reset($name = NULL);
    *   The old name of the configuration object.
    * @param string $new_name
    *   The new name of the configuration object.
+   * @param bool $mutable
+   *   (optional) Create an mutable configuration object. Defaults to TRUE.
    *
    * @return \Drupal\Core\Config\Config
    *   The renamed config object.
    */
-  public function rename($old_name, $new_name);
+  public function rename($old_name, $new_name, $mutable = TRUE);
 
   /**
    * The cache keys associated with the state of the config factory.
diff --git a/core/lib/Drupal/Core/Config/ImmutableConfig.php b/core/lib/Drupal/Core/Config/ImmutableConfig.php
new file mode 100644
index 0000000..90302cb
--- /dev/null
+++ b/core/lib/Drupal/Core/Config/ImmutableConfig.php
@@ -0,0 +1,42 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Config\ImmutableConfig.
+ */
+
+namespace Drupal\Core\Config;
+
+use Drupal\Component\Utility\String;
+
+class ImmutableConfig extends Config {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function set($key, $value) {
+    throw new ImmutableConfigException(String::format('@config_name:@key cannot be set on an immutable object', array('@config_name' => $this->getName(), '@key' => $key)));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function clear($key) {
+    throw new ImmutableConfigException(String::format('@config_name:@key cannot be cleared on an immutable object', array('@config_name' => $this->getName(), '@key' => $key)));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function save() {
+    throw new ImmutableConfigException(String::format('@config_name cannot be saved, it is an immutable object', array('@config_name' => $this->getName())));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function delete() {
+    throw new ImmutableConfigException(String::format('@config_name cannot be deleted, it is an immutable object', array('@config_name' => $this->getName())));
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Config/ImmutableConfigException.php b/core/lib/Drupal/Core/Config/ImmutableConfigException.php
new file mode 100644
index 0000000..fca05a3
--- /dev/null
+++ b/core/lib/Drupal/Core/Config/ImmutableConfigException.php
@@ -0,0 +1,12 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Config\ImmutableConfigException.
+ */
+
+namespace Drupal\Core\Config;
+
+
+class ImmutableConfigException extends \RuntimeException {
+}
diff --git a/core/lib/Drupal/Core/Form/FormBase.php b/core/lib/Drupal/Core/Form/FormBase.php
index 3a14612..3039fb9 100644
--- a/core/lib/Drupal/Core/Form/FormBase.php
+++ b/core/lib/Drupal/Core/Form/FormBase.php
@@ -80,11 +80,12 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
    *   the config object returned will contain the contents of book.admin
    *   configuration file.
    *
-   * @return \Drupal\Core\Config\Config
-   *   A configuration object.
+   * @return \Drupal\Core\Config\ImmutableConfig
+   *   A configuration object which cannot be changed. If the form is saving
+   *   configuration \Drupal\Core\Form\ConfigFormBase is preferred.
    */
   protected function config($name) {
-    return $this->configFactory()->get($name);
+    return $this->configFactory()->get($name, FALSE);
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
index 750e967..ba55764 100644
--- a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
@@ -8,7 +8,7 @@
 namespace Drupal\Core\Installer\Form;
 
 use Drupal\Core\Extension\ModuleInstallerInterface;
-use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\ConfigFormBase;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Locale\CountryManagerInterface;
 use Drupal\Core\State\StateInterface;
@@ -18,7 +18,7 @@
 /**
  * Provides the site configuration form.
  */
-class SiteConfigureForm extends FormBase {
+class SiteConfigureForm extends ConfigFormBase {
 
   /**
    * The user storage.
diff --git a/core/lib/Drupal/Core/Menu/StaticMenuLinkOverrides.php b/core/lib/Drupal/Core/Menu/StaticMenuLinkOverrides.php
index ebde906..4c4370b 100644
--- a/core/lib/Drupal/Core/Menu/StaticMenuLinkOverrides.php
+++ b/core/lib/Drupal/Core/Menu/StaticMenuLinkOverrides.php
@@ -80,7 +80,9 @@ public function loadOverride($id) {
    * {@inheritdoc}
    */
   public function deleteMultipleOverrides(array $ids) {
-    $all_overrides = $this->getConfig()->get('definitions');
+    // Get the original configuration without overrides to ensure that global
+    // overrides are saved to configuration.
+    $all_overrides = $this->getConfig()->getOriginal('definitions', FALSE);
     $save = FALSE;
     foreach ($ids as $id) {
       $id = static::encodeId($id);
@@ -134,11 +136,15 @@ public function saveOverride($id, array $definition) {
     // Filter the overrides to only those that are expected.
     $definition = array_intersect_key($definition, $expected);
     if ($definition) {
-      $id = static::encodeId($id);
-      $all_overrides = $this->getConfig()->get('definitions');
-      // Combine with any existing data.
-      $all_overrides[$id] = $definition + $this->loadOverride($id);
-      $this->getConfig()->set('definitions', $all_overrides)->save();
+      $config_key = 'definitions.' . static::encodeId($id);
+      // Get the original configuration without overrides to ensure that global
+      // overrides are saved to configuration.
+      $existing_override = $this->getConfig()->getOriginal($config_key, FALSE);
+      if ($existing_override) {
+        // Combine with any existing data.
+        $definition += $existing_override;
+      }
+      $this->getConfig()->set($config_key, $definition)->save();
     }
     return array_keys($definition);
   }
diff --git a/core/modules/config/src/Form/ConfigSingleImportForm.php b/core/modules/config/src/Form/ConfigSingleImportForm.php
index 58156b0..d67fc12 100644
--- a/core/modules/config/src/Form/ConfigSingleImportForm.php
+++ b/core/modules/config/src/Form/ConfigSingleImportForm.php
@@ -265,4 +265,20 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
     }
   }
 
+  /**
+   * {@inheritdoc}
+   *
+   * Overrides \Drupal\Core\Form\FormBase::config() so that configuration is
+   * returned override free. This ensures that overrides do not pollute saved
+   * configuration.
+   */
+  protected function config($name) {
+    $config_factory = $this->configFactory();
+    $old_state = $config_factory->getOverrideState();
+    $config_factory->setOverrideState(FALSE);
+    $config = $config_factory->get($name);
+    $config_factory->setOverrideState($old_state);
+    return $config;
+  }
+
 }
diff --git a/core/modules/contact/src/ContactFormEditForm.php b/core/modules/contact/src/ContactFormEditForm.php
index 123ba38..ffda57f 100644
--- a/core/modules/contact/src/ContactFormEditForm.php
+++ b/core/modules/contact/src/ContactFormEditForm.php
@@ -7,9 +7,11 @@
 
 namespace Drupal\contact;
 
+use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Form\FormStateInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
  * Base form for contact form edit forms.
@@ -17,13 +19,39 @@
 class ContactFormEditForm extends EntityForm {
 
   /**
+   * The config factory.
+   *
+   * @var \Drupal\Core\Config\ConfigFactoryInterface
+   */
+  protected $configFactory;
+
+  /**
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   *   The config factory.
+   */
+  public function __construct(ConfigFactoryInterface $config_factory) {
+    $this->configFactory = $config_factory;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('config.factory')
+    );
+  }
+
+  /**
    * {@inheritdoc}
    */
   public function form(array $form, FormStateInterface $form_state) {
     $form = parent::form($form, $form_state);
 
     $contact_form = $this->entity;
-    $default_form = $this->config('contact.settings')->get('default_form');
+    // Get value without any overrides so we don't copy overrides into active
+    // configuration.
+    $default_form = $this->configFactory->get('contact.settings')->getOriginal('default_form', FALSE);
 
     $form['label'] = array(
       '#type' => 'textfield',
@@ -94,7 +122,7 @@ public function validate(array $form, FormStateInterface $form_state) {
   public function save(array $form, FormStateInterface $form_state) {
     $contact_form = $this->entity;
     $status = $contact_form->save();
-    $contact_settings = $this->config('contact.settings');
+    $contact_settings = $this->configFactory->get('contact.settings');
 
     $edit_link = $this->entity->link($this->t('Edit'));
     if ($status == SAVED_UPDATED) {
diff --git a/core/modules/system/src/Form/ThemeAdminForm.php b/core/modules/system/src/Form/ThemeAdminForm.php
index 2cee8c5..93cace8 100644
--- a/core/modules/system/src/Form/ThemeAdminForm.php
+++ b/core/modules/system/src/Form/ThemeAdminForm.php
@@ -6,13 +6,13 @@
 
 namespace Drupal\system\Form;
 
-use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\ConfigFormBase;
 use Drupal\Core\Form\FormStateInterface;
 
 /**
  * Form to select the administration theme.
  */
-class ThemeAdminForm extends FormBase {
+class ThemeAdminForm extends ConfigFormBase {
 
   /**
    * {@inheritdoc}
@@ -50,7 +50,7 @@ public function buildForm(array $form, FormStateInterface $form_state, array $th
    * {@inheritdoc}
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
-    drupal_set_message($this->t('The configuration options have been saved.'));
+    parent::submitForm($form, $form_state);
     $this->config('system.theme')->set('admin', $form_state->getValue('admin_theme'))->save();
   }
 
diff --git a/core/modules/system/tests/modules/form_test/src/FormTestArgumentsObject.php b/core/modules/system/tests/modules/form_test/src/FormTestArgumentsObject.php
index da7b4d5..3f56422 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestArgumentsObject.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestArgumentsObject.php
@@ -55,7 +55,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
     drupal_set_message($this->t('The FormTestArgumentsObject::submitForm() method was used for this form.'));
-    $this->config('form_test.object')
+    $this->configFactory()->get('form_test.object')
       ->set('bananas', $form_state->getValue('bananas'))
       ->save();
   }
diff --git a/core/modules/system/tests/modules/form_test/src/FormTestControllerObject.php b/core/modules/system/tests/modules/form_test/src/FormTestControllerObject.php
index a3e5064..ae58495 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestControllerObject.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestControllerObject.php
@@ -65,7 +65,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
     drupal_set_message($this->t('The FormTestControllerObject::submitForm() method was used for this form.'));
-    $this->config('form_test.object')
+    $this->configFactory()->get('form_test.object')
       ->set('bananas', $form_state->getValue('bananas'))
       ->save();
   }
diff --git a/core/modules/system/tests/modules/form_test/src/FormTestObject.php b/core/modules/system/tests/modules/form_test/src/FormTestObject.php
index 4669bfe..0274a91 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestObject.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestObject.php
@@ -56,7 +56,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
     drupal_set_message($this->t('The FormTestObject::submitForm() method was used for this form.'));
-    $this->config('form_test.object')
+    $this->configFactory()->get('form_test.object')
       ->set('bananas', $form_state->getValue('bananas'))
       ->save();
   }
diff --git a/core/modules/system/tests/modules/form_test/src/FormTestServiceObject.php b/core/modules/system/tests/modules/form_test/src/FormTestServiceObject.php
index de4e6c0..30587df 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestServiceObject.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestServiceObject.php
@@ -54,7 +54,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
     drupal_set_message($this->t('The FormTestServiceObject::submitForm() method was used for this form.'));
-    $this->config('form_test.object')
+    $this->configFactory()->get('form_test.object')
       ->set('bananas', $form_state->getValue('bananas'))
       ->save();
   }
diff --git a/core/tests/Drupal/Tests/Core/Config/Entity/ConfigEntityStorageTest.php b/core/tests/Drupal/Tests/Core/Config/Entity/ConfigEntityStorageTest.php
index ddfbd81..2e07572 100644
--- a/core/tests/Drupal/Tests/Core/Config/Entity/ConfigEntityStorageTest.php
+++ b/core/tests/Drupal/Tests/Core/Config/Entity/ConfigEntityStorageTest.php
@@ -722,7 +722,7 @@ public function testDelete() {
       $config_object->expects($this->once())
         ->method('delete');
       $configs[] = $config_object;
-      $config_map[] = array("the_config_prefix.$id", $config_object);
+      $config_map[] = array("the_config_prefix.$id", TRUE, $config_object);
     }
 
     $this->cacheBackend->expects($this->once())
diff --git a/core/tests/Drupal/Tests/Core/Menu/StaticMenuLinkOverridesTest.php b/core/tests/Drupal/Tests/Core/Menu/StaticMenuLinkOverridesTest.php
index c436d6f..cb554fe 100644
--- a/core/tests/Drupal/Tests/Core/Menu/StaticMenuLinkOverridesTest.php
+++ b/core/tests/Drupal/Tests/Core/Menu/StaticMenuLinkOverridesTest.php
@@ -105,41 +105,31 @@ public function testSaveOverride() {
     $config = $this->getMockBuilder('Drupal\Core\Config\Config')
       ->disableOriginalConstructor()
       ->getMock();
+
+    $definition_test1 = array('parent' => 'test0');
+    $definition_test2 = array('parent' => 'test1');
+
     $config->expects($this->at(0))
-      ->method('get')
-      ->with('definitions')
-      ->will($this->returnValue(array()));
+      ->method('getOriginal')
+      ->with('definitions.test1', FALSE)
+      ->willReturn(FALSE);
     $config->expects($this->at(1))
-      ->method('get')
-      ->with('definitions')
-      ->will($this->returnValue(array()));
-
-    $definition_save_1 = array('definitions' => array('test1' => array('parent' => 'test0')));
-    $definitions_save_2 = array(
-      'definitions' => array(
-        'test1' => array('parent' => 'test0'),
-        'test1__la___ma' => array('parent' => 'test1')
-      )
-    );
-    $config->expects($this->at(2))
       ->method('set')
-      ->with('definitions', $definition_save_1['definitions'])
-      ->will($this->returnSelf());
-    $config->expects($this->at(3))
+      ->with('definitions.test1', $definition_test1)
+      ->willReturnSelf();
+    $config->expects($this->at(2))
       ->method('save');
+    // Ensure that existing values are merge in and that IDs are massaged to
+    // work in configuration.
+    $config->expects($this->at(3))
+      ->method('getOriginal')
+      ->with('definitions.test1__la___ma', FALSE)
+      ->willReturn(array('weight' => 5));
     $config->expects($this->at(4))
-      ->method('get')
-      ->with('definitions')
-      ->will($this->returnValue($definition_save_1['definitions']));
-    $config->expects($this->at(5))
-      ->method('get')
-      ->with('definitions')
-      ->will($this->returnValue($definition_save_1['definitions']));
-    $config->expects($this->at(6))
       ->method('set')
-      ->with('definitions', $definitions_save_2['definitions'])
-      ->will($this->returnSelf());
-    $config->expects($this->at(7))
+      ->with('definitions.test1__la___ma', $definition_test2 + array('weight' => 5))
+      ->willReturnSelf();
+    $config->expects($this->at(5))
       ->method('save');
 
     $config_factory = $this->getMock('Drupal\Core\Config\ConfigFactoryInterface');
@@ -149,8 +139,11 @@ public function testSaveOverride() {
 
     $static_override = new StaticMenuLinkOverrides($config_factory);
 
-    $static_override->saveOverride('test1', array('parent' => 'test0'));
-    $static_override->saveOverride('test1.la__ma', array('parent' => 'test1'));
+    $properties = $static_override->saveOverride('test1', $definition_test1);
+    $this->assertEquals(['parent'], $properties);
+
+    $properties = $static_override->saveOverride('test1.la__ma', $definition_test2);
+    $this->assertEquals(['parent', 'weight'], $properties);
   }
 
   /**
@@ -170,8 +163,8 @@ public function testDeleteOverrides($ids, array $old_definitions, array $new_def
       ->disableOriginalConstructor()
       ->getMock();
     $config->expects($this->at(0))
-      ->method('get')
-      ->with('definitions')
+      ->method('getOriginal')
+      ->with('definitions', FALSE)
       ->will($this->returnValue($old_definitions));
 
     // Only save if the definitions changes.
diff --git a/core/tests/Drupal/Tests/UnitTestCase.php b/core/tests/Drupal/Tests/UnitTestCase.php
index 43748e8..430b468 100644
--- a/core/tests/Drupal/Tests/UnitTestCase.php
+++ b/core/tests/Drupal/Tests/UnitTestCase.php
@@ -119,7 +119,7 @@ public function getConfigFactoryStub(array $configs = array()) {
         ->method('get')
         ->will($this->returnValueMap($map));
 
-      $config_map[] = array($config_name, $config_object);
+      $config_map[] = array($config_name, TRUE, $config_object);
     }
     // Construct a config factory with the array of configuration object stubs
     // as its return map.