diff -u b/core/includes/install.inc b/core/includes/install.inc
--- b/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -412,7 +412,10 @@
   if ($system_versions = drupal_get_schema_versions('system')) {
     KeyValueFactory::get('system.module.schema')->set('system', max($system_versions));
   }
-  module_config()->set('system', 0)->save();
+  config('system.module')
+    ->set('system', 0)
+    ->setSorter('module_config_sort')
+    ->save();
 
   // Clear out module list and hook implementation statics before calling
   // system_rebuild_theme_data().
diff -u b/core/includes/module.inc b/core/includes/module.inc
--- b/core/includes/module.inc
+++ b/core/includes/module.inc
@@ -135,7 +135,7 @@
       }
     }
     else {
-      $enabled_modules = module_config()->get();
+      $enabled_modules = config('system.module')->get();
       _system_list_warm('module', 'system', 'core/modules/system.module', TRUE);
       $module_data = system_rebuild_module_data();
       $bootstrap_list = array();
@@ -167,7 +167,7 @@
       // locations in the file system. The ordering here must also be
       // consistent with the one used in module_implements().
       $enabled_themes = config('system.theme')->get();
-      $enabled_modules = module_config()->get();
+      $enabled_modules = config('system.module')->get();
       // It's important to retrieve these first because the rebuild calls
       // reset the system_list static.
       _system_list_warm('module', 'system', 'core/modules/system.module', TRUE);
@@ -453,7 +453,7 @@
   $schema_store = KeyValueFactory::get('system.module.schema');
   $weight_store = KeyValueFactory::get('system.module.weight');
   foreach ($module_list as $module) {
-    $config = module_config();
+    $config = config('system.module');
     // Only process modules that are not already enabled.
     $enabled = TRUE;
     if (!$schema_store->get($module)) {
@@ -467,6 +467,7 @@
     if (!$enabled) {
       $config
         ->set($module, $weight)
+        ->setSorter('module_config_sort')
         ->save();
       if ($weight) {
         $weight_store->delete($module_list);
@@ -583,7 +584,7 @@
   $store = KeyValueFactory::get('system.module.weight');
   foreach ($module_list as $module) {
     if (module_exists($module)) {
-      $config = module_config();
+      $config = config('system.module');
       module_load_install($module);
       module_invoke($module, 'disable');
       if ($weight = $config->get($module)) {
@@ -591,6 +592,7 @@
       }
       $config
         ->clear($module)
+        ->setSorter('module_config_sort')
         ->save();
       $invoke_modules[] = $module;
       watchdog('system', '%module module disabled.', array('%module' => $module), WATCHDOG_INFO);
@@ -1149,21 +1151,27 @@
-/**
- * Retrieves the module list configuration object.
- *
- * @return Drupal\Core\Config\ModuleConfig
- *   A configuration object.
- */
-function module_config() {
-  return drupal_container()->get('config.factory')->get('system.module', 'Drupal\Core\Config\ModuleConfig')->load();
-}
-
 function module_set_weight($module, $weight) {
-  $config = module_config();
+  $config = config('system.module');
   if ($config->get($module) !== NULL) {
     $config
       ->set($module, $weight)
+      ->setSorter('module_config_sort')
       ->save();
   }
   else {
     KeyValueFactory::get('system.module.weight')->set($module, $weight);
   }
 }
+
+function module_config_sort($data) {
+  $sort = array();
+  foreach ($data as $name => $weight) {
+    // We can't use the sign directly because + (ASCII 43) is before
+    // - (ASCII 45). So negative nubmers get a 0, non-negative numbers
+    // a 1 prefix.
+    $prefix = (int) ($weight >= 0);
+    // PHP_INT_MAX is at most 19 characters so make every number equally
+    // 19 digits long.
+    $sort[] = $prefix . sprintf('%019d', abs($weight)) . $name;
+  }
+  array_multisort($sort, SORT_STRING, $data);
+  return $data;
+}
\ No newline at end of file
diff -u b/core/includes/theme.inc b/core/includes/theme.inc
--- b/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1394,7 +1394,7 @@
   drupal_clear_css_cache();
   $config = config('system.theme');
   foreach ($theme_list as $key) {
-    // The value is not used, it needs to be consisent with
+    // The value is not used, it needs to be consistent with
     // config('system.module') which uses the value for weight so set all of
     // them to the same value. 1 looks like 'enabled' so let's use that.
     $config->set($key, 1);
diff -u b/core/includes/update.inc b/core/includes/update.inc
--- b/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -28,7 +28,7 @@
  */
 function update_fix_compatibility() {
   foreach (array('module', 'theme') as $type) {
-    $config = $type == 'module' ? module_config() : config('system.theme');
+    $config = config("system.$type");
     $save = FALSE;
     foreach ($config->get() as $name => $weight) {
       if (update_check_incompatibility($name, $type)) {
@@ -37,6 +37,9 @@
       }
     }
     if ($save) {
+      if ($type == 'module') {
+        $config->setSorter('module_config_sort');
+      }
       $config->save();
     }
   }
@@ -176,7 +179,7 @@
       // web server, an exception will be thrown, halting the update.
       drupal_install_config_directories();
       $configs = array(
-        'module' => module_config(),
+        'module' => config('system.module'),
         'theme' => config('system.theme'),
       );
       $schema_store = KeyValueFactory::get('system.module.schema');
@@ -198,6 +201,7 @@
           }
         }
       }
+      $configs['module']->setSorter('module_config_sort');
       foreach ($configs as $config) {
         $config->save();
       }
@@ -400,7 +404,10 @@
       }
     }
     // Enable the module with a weight of 0.
-    module_config()->set($module, 0)->save();
+    config('system.module')
+      ->set($module, 0)
+      ->setSorter('module_config_sort')
+      ->save();
     // Change the schema version from SCHEMA_UNINSTALLED to 0, so any module
     // updates since the module's inception are executed in a core upgrade.
     $store->set($module, 0);
diff -u b/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
--- b/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -64,10 +64,21 @@
    */
   protected $eventDispatcher;
 
-
+  /**
+   * TRUE if the configuration object does not need sorting on save.
+   *
+   * @var bool
+   */
   protected $sorted = FALSE;
 
   /**
+   * The callable that sorts the data before save.
+   *
+   * @var callable
+   */
+  protected $sorter;
+
+  /**
    * Constructs a configuration object.
    *
    * @param string $name
@@ -314,7 +325,7 @@
    */
   public function save() {
     if (!$this->sorted) {
-      $this->sortByKey($this->data);
+      call_user_func($this->sorter ? $this->sorter : array($this, 'sortByKey'), $this->data);
     }
     $this->storage->write($this->name, $this->data);
     $this->isNew = FALSE;
@@ -340,6 +351,14 @@
   }
 
   /**
+   * @param callable
+   */
+  function setSorter($sorter) {
+    $this->sorter = $sorter;
+    return $this;
+  }
+
+  /**
    * Sorts all keys in configuration data.
    *
    * Ensures that re-inserted keys appear in the same location as before, in
@@ -350,13 +369,14 @@
    * @param array $data
    *   An associative array to sort recursively by key name.
    */
-  public function sortByKey(array &$data) {
+  public function sortByKey(array $data) {
     ksort($data);
     foreach ($data as &$value) {
       if (is_array($value)) {
-        $this->sortByKey($value);
+        $value = $this->sortByKey($value);
       }
     }
+    return $data;
   }
 
   /**
reverted:
--- b/core/lib/Drupal/Core/Config/ConfigFactory.php
+++ a/core/lib/Drupal/Core/Config/ConfigFactory.php
@@ -57,13 +57,11 @@
    *
    * @param string $name
    *   The name of the configuration object to construct.
-   * @param $class_name
-   *   Optional. The name of the class handling this configuration object.
    *
    * @return Drupal\Core\Config\Config
    *   A configuration object with the given $name.
    */
+  public function get($name) {
-  public function get($name, $class_name = 'Drupal\Core\Config\Config') {
     global $conf;
 
     // @todo Caching the instantiated objects per name might cut off a fair
@@ -84,7 +82,7 @@
     // @todo The decrease of CPU time is interesting, since that means that
     //   ContainerBuilder involves plenty of function calls (which are known to
     //   be slow in PHP).
+    $config = new Config($name, $this->storage, $this->eventDispatcher);
-    $config = new $class_name($name, $this->storage, $this->eventDispatcher);
     return $config->init();
   }
 
reverted:
--- b/core/lib/Drupal/Core/Config/ModuleConfig.php
+++ /dev/null
@@ -1,34 +0,0 @@
-<?php
-/**
- * @file
- * Definition of Drupal\Core\Config\ModuleConfig.
- */
-
-namespace Drupal\Core\Config;
-
-/**
- * Defines the module configuration object.
- */
-class ModuleConfig extends Config {
-
-  public function save() {
-    if ($this->data) {
-      $sort = array();
-      foreach ($this->data as $name => $weight) {
-        // We can't use the sign directly because + (ASCII 43) is before
-        // - (ASCII 45). So negative nubmers get a 0, non-negative numbers
-        // a 1 prefix.
-        $prefix = (int) ($weight >= 0);
-        // PHP_INT_MAX is at most 19 characters so make every number equally
-        // 19 digits long.
-        $sort[] = $prefix . sprintf('%019d', abs($weight)) . $name;
-      }
-      array_multisort($sort, SORT_STRING, $this->data);
-    }
-    $this->storage->write($this->name, $this->data);
-    $this->isNew = FALSE;
-    $this->notify('save');
-    return $this;
-  }
-
-}
diff -u b/core/modules/field/field.module b/core/modules/field/field.module
--- b/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -364,7 +364,7 @@
       }
       if ($non_deleted) {
         // Calling module_exists() here leads to infinite recursion.
-        if (module_config()->get('field_ui') !== NULL) {
+        if (config('system.module')->get('field_ui') !== NULL) {
           $explanation = t('Field type(s) in use - see <a href="@fields-page">Field list</a>', array('@fields-page' => url('admin/reports/fields')));
         }
         else {
diff -u b/core/modules/help/lib/Drupal/help/Tests/HelpTest.php b/core/modules/help/lib/Drupal/help/Tests/HelpTest.php
--- b/core/modules/help/lib/Drupal/help/Tests/HelpTest.php
+++ b/core/modules/help/lib/Drupal/help/Tests/HelpTest.php
@@ -109,7 +109,7 @@
   protected function getModuleList() {
     $modules = array();
     $module_data = system_rebuild_module_data();
-    foreach (module_config()->get() as $module => $data) {
+    foreach (config('system.module')->get() as $module => $data) {
       if (file_exists($module_data[$module]->filename) && function_exists($module . '_help')) {
         $modules[$module] = $module_data[$module]->info['name'];
       }
diff -u b/core/modules/system/lib/Drupal/system/Tests/Upgrade/UpgradePathTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Upgrade/UpgradePathTestBase.php
--- b/core/modules/system/lib/Drupal/system/Tests/Upgrade/UpgradePathTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Upgrade/UpgradePathTestBase.php
@@ -275,11 +275,13 @@
 
     $config = config('system.module');
     foreach ($config->get() as $module => $data) {
-      if (!in_array($module, $required_modules)) {
+      if (!in_array($module, $modules)) {
         $config->clear($module);
       }
     }
-    $config->save();
+    $config
+      ->setSorter('module_config_sort')
+      ->save();
   }
 
 }
diff -u b/core/modules/system/system.module b/core/modules/system/system.module
--- b/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -2810,7 +2810,7 @@
       $modules[$module]->weight = $weight;
     }
     // Enabled status and weights.
-    foreach (module_config()->get() as $module => $weight) {
+    foreach (config('system.module')->get() as $module => $weight) {
       $modules[$module]->status = 1;
       $modules[$module]->weight = $weight;
     }
@@ -2828,7 +2828,7 @@
     $type = 'module';
     // It is not impossible a function resets the modules cache. Keep it.
     $modules = $modules_cache['data'];
-    foreach (module_config()->get() as $module => $weight) {
+    foreach (config('system.module')->get() as $module => $weight) {
       $function = $module .'_system_info_alter';
       if (function_exists($function)) {
         foreach ($modules as $record) {
diff -u b/core/modules/update/lib/Drupal/update/Tests/UpdateContribTest.php b/core/modules/update/lib/Drupal/update/Tests/UpdateContribTest.php
--- b/core/modules/update/lib/Drupal/update/Tests/UpdateContribTest.php
+++ b/core/modules/update/lib/Drupal/update/Tests/UpdateContribTest.php
@@ -210,7 +210,9 @@
         $config->clear($theme);
       }
     }
-    $config->save();
+    $config
+        ->setSorter('module_config_sort')
+        ->save();
 
     // Define the initial state for core and the test contrib themes.
     $system_info = array(