diff --git a/core/includes/form.inc b/core/includes/form.inc
index 362d0d5..9cfcad2 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -2002,6 +2002,10 @@ function _form_builder_handle_input_element($form_id, &$element, &$form_state) {
   // submitted with drupal_form_submit() may bypass access restriction and be
   // treated as high-privilege users instead.
   $process_input = empty($element['#disabled']) && ($form_state['programmed'] || ($form_state['process_input'] && (!isset($element['#access']) || $element['#access'])));
+  $loadable = isset($element['#load']) && isset($form_state['callbacks']['load'][$element['#load']]);
+  if ($loadable) {
+    $form_state['loadables'][$element['#load']][] = $element['#array_parents'];
+  }
 
   // Set the element's #value property.
   if (!isset($element['#value']) && !array_key_exists('#value', $element)) {
@@ -2043,6 +2047,10 @@ function _form_builder_handle_input_element($form_id, &$element, &$form_state) {
     }
     // Load defaults.
     if (!isset($element['#value'])) {
+      if ($loadable) {
+        $function = $form_state['callbacks']['load'][$element['#load']];
+        $element['#default_value'] = $function($element);
+      }
       // Call #type_value without a second argument to request default_value handling.
       if (function_exists($value_callback)) {
         $element['#value'] = $value_callback($element, FALSE, $form_state);
diff --git a/core/modules/aggregator/aggregator.admin.inc b/core/modules/aggregator/aggregator.admin.inc
index 718e79c..25fa8ce 100644
--- a/core/modules/aggregator/aggregator.admin.inc
+++ b/core/modules/aggregator/aggregator.admin.inc
@@ -428,14 +428,15 @@ function aggregator_admin_refresh_feed($feed) {
  * @see aggregator_admin_form_submit()
  * @ingroup forms
  */
-function aggregator_admin_form($form, $form_state) {
+function aggregator_admin_form($form, &$form_state) {
   // Global aggregator settings.
   $form['aggregator_allowed_html_tags'] = array(
     '#type' => 'textfield',
     '#title' => t('Allowed HTML tags'),
     '#size' => 80,
     '#maxlength' => 255,
-    '#default_value' => config('aggregator.settings')->get('items.allowed_html'),
+    '#load' => 'config',
+    '#config_key' => 'items.allowed_html',
     '#description' => t('A space-separated list of HTML tags allowed in the content of feed items. Disallowed tags are stripped from the content.'),
   );
 
@@ -484,7 +485,8 @@ function aggregator_admin_form($form, $form_state) {
       '#title' => t('Fetcher'),
       '#description' => t('Fetchers download data from an external source. Choose a fetcher suitable for the external source you would like to download from.'),
       '#options' => $fetchers,
-      '#default_value' => config('aggregator.settings')->get('fetcher'),
+      '#load' => 'config',
+      '#config_key' => 'fetcher',
     );
   }
   if (count($parsers) > 1) {
@@ -493,7 +495,8 @@ function aggregator_admin_form($form, $form_state) {
       '#title' => t('Parser'),
       '#description' => t('Parsers transform downloaded data into standard structures. Choose a parser suitable for the type of feeds you would like to aggregate.'),
       '#options' => $parsers,
-      '#default_value' => config('aggregator.settings')->get('parser'),
+      '#load' => 'config',
+      '#config_key' => 'parser',
     );
   }
   if (count($processors) > 1) {
@@ -502,7 +505,8 @@ function aggregator_admin_form($form, $form_state) {
       '#title' => t('Processors'),
       '#description' => t('Processors act on parsed feed data, for example they store feed items. Choose the processors suitable for your task.'),
       '#options' => $processors,
-      '#default_value' => config('aggregator.settings')->get('processors'),
+      '#load' => 'config',
+      '#config_key' => 'processors',
     );
   }
   if (count($basic_conf)) {
@@ -518,35 +522,12 @@ function aggregator_admin_form($form, $form_state) {
 
   // Implementing modules will expect an array at $form['modules'].
   $form['modules'] = array();
+  $form['#config'] = config('aggregator.settings');
 
   return system_config_form($form, $form_state);
 }
 
 /**
- * Form submission handler for aggregator_admin_form().
- */
-function aggregator_admin_form_submit($form, &$form_state) {
-  $config = config('aggregator.settings');
-  $config
-    ->set('items.allowed_html', $form_state['values']['aggregator_allowed_html_tags'])
-    ->set('items.expire', $form_state['values']['aggregator_clear'])
-    ->set('items.teaser_length', $form_state['values']['aggregator_teaser_length'])
-    ->set('source.list_max', $form_state['values']['aggregator_summary_items'])
-    ->set('source.category_selector', $form_state['values']['aggregator_category_selector']);
-
-  if (isset($form_state['values']['aggregator_fetcher'])) {
-    $config->set('fetcher', $form_state['values']['aggregator_fetcher']);
-  }
-  if (isset($form_state['values']['aggregator_parser'])) {
-    $config->set('parser', $form_state['values']['aggregator_parser']);
-  }
-  if (isset($form_state['values']['aggregator_processors'])) {
-    $config->set('processors', array_filter($form_state['values']['aggregator_processors']));
-  }
-  $config->save();
-}
-
-/**
  * Form constructor to add/edit/delete aggregator categories.
  *
  * @param $edit
diff --git a/core/modules/aggregator/aggregator.processor.inc b/core/modules/aggregator/aggregator.processor.inc
index c12c90f..4303618 100644
--- a/core/modules/aggregator/aggregator.processor.inc
+++ b/core/modules/aggregator/aggregator.processor.inc
@@ -95,7 +95,8 @@ function aggregator_form_aggregator_admin_form_alter(&$form, $form_state) {
     $form['modules']['aggregator']['aggregator_summary_items'] = array(
       '#type' => 'select',
       '#title' => t('Number of items shown in listing pages'),
-      '#default_value' => config('aggregator.settings')->get('source.list_max'),
+      '#load' => 'config',
+      '#config_key' => 'source.list_max',
       '#empty_value' => 0,
       '#options' => $items,
     );
@@ -103,7 +104,8 @@ function aggregator_form_aggregator_admin_form_alter(&$form, $form_state) {
     $form['modules']['aggregator']['aggregator_clear'] = array(
       '#type' => 'select',
       '#title' => t('Discard items older than'),
-      '#default_value' => config('aggregator.settings')->get('items.expire'),
+      '#load' => 'config',
+      '#config_key' => 'items.expire',
       '#options' => $period,
       '#description' => t('Requires a correctly configured <a href="@cron">cron maintenance task</a>.', array('@cron' => url('admin/reports/status'))),
     );
@@ -111,7 +113,8 @@ function aggregator_form_aggregator_admin_form_alter(&$form, $form_state) {
     $form['modules']['aggregator']['aggregator_category_selector'] = array(
       '#type' => 'radios',
       '#title' => t('Select categories using'),
-      '#default_value' => config('aggregator.settings')->get('source.category_selector'),
+      '#load' => 'config',
+      '#config_key' => 'source.category_selector',
       '#options' => array('checkboxes' => t('checkboxes'),
       'select' => t('multiple selector')),
       '#description' => t('For a small number of categories, checkboxes are easier to use, while a multiple selector works well with large numbers of categories.'),
@@ -119,7 +122,8 @@ function aggregator_form_aggregator_admin_form_alter(&$form, $form_state) {
     $form['modules']['aggregator']['aggregator_teaser_length'] = array(
       '#type' => 'select',
       '#title' => t('Length of trimmed description'),
-      '#default_value' => config('aggregator.settings')->get('items.teaser_length'),
+      '#load' => 'config',
+      '#config_key' => 'items.teaser_length',
       '#options' => drupal_map_assoc(array(0, 200, 400, 600, 800, 1000, 1200, 1400, 1600, 1800, 2000), '_aggregator_characters'),
       '#description' => t("The maximum number of characters used in the trimmed version of content.")
     );
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Tests/AggregatorConfigurationTest.php b/core/modules/aggregator/lib/Drupal/aggregator/Tests/AggregatorConfigurationTest.php
index 65eb6ab..0ffa9a9 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Tests/AggregatorConfigurationTest.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Tests/AggregatorConfigurationTest.php
@@ -34,7 +34,7 @@ class AggregatorConfigurationTest extends AggregatorTestBase {
     $this->assertText(t('The configuration options have been saved.'));
 
     foreach ($edit as $name => $value) {
-      $this->assertFieldByName($name, $value, t('"@name" has correct default value.', array('@name' => $name)));
+      $this->assertFieldByName($name, $value, t('"@name" has correct default value: @value.', array('@name' => $name, '@value' => $value)));
     }
   }
 }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index de7241f..f87c97b 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -6,6 +6,7 @@
  */
 
 use Drupal\Core\Utility\ModuleInfo;
+use Drupal\Component\Utility\NestedArray;
 
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\Response;
@@ -3111,6 +3112,12 @@ function system_config_form($form, &$form_state) {
   if (!isset($form['#theme'])) {
     $form['#theme'] = 'system_settings_form';
   }
+  if (isset($form['#config'])) {
+    $config = $form['#config'];
+    $form_state['callbacks']['load']['config'] = function ($element) use ($config) {
+      return $config->get($element['#config_key']);
+    };
+  }
   return $form;
 }
 
@@ -3120,6 +3127,15 @@ function system_config_form($form, &$form_state) {
  * @see system_config_form()
  */
 function system_config_form_submit($form, &$form_state) {
+  if (isset($form['#config'])) {
+    $config = $form['#config'];
+    foreach ($form_state['loadables']['config'] as $parents) {
+      $element = NestedArray::getValue($form, $parents);
+      $value = ($element['#type'] == 'checkboxes') ? array_keys(array_filter($element['#value'])) : $element['#value'];
+      $config->set($element['#config_key'], $value);
+    }
+    $config->save();
+  }
   drupal_set_message(t('The configuration options have been saved.'));
 }