diff --git a/core/core.services.yml b/core/core.services.yml
index ed1341c..cd7833e 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1505,6 +1505,12 @@ services:
       - { name: event_subscriber }
   email.validator:
     class: Egulias\EmailValidator\EmailValidator
+  update.post_update_registry:
+    class: Drupal\Core\Update\UpdateRegistry
+    factory: ['@update.post_update_registry_factory', configure]
+  update.post_update_registry_factory:
+    class: Drupal\Core\Update\UpdateRegistryFactory
+    parent: container.trait
 
   response_filter.active_link:
     class: Drupal\Core\EventSubscriber\ActiveLinkResponseFilter
diff --git a/core/includes/update.inc b/core/includes/update.inc
index 3695a92..b6b5bc8 100644
--- a/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -242,14 +242,11 @@ function update_invoke_post_update($function, &$context) {
       $ret['results']['query'] = $function($context['sandbox']);
       $ret['results']['success'] = TRUE;
 
-      $key_value_store = \Drupal::keyValue('update__post_update');
-      $executed_updates = $key_value_store->get('existing_updates', []);
-      $executed_updates[] = $function;
-      $key_value_store->set('existing_updates', $executed_updates);
+      \Drupal::service('update.post_update_registry')->registerInvokedUpdate($function);
     }
-      // @TODO We may want to do different error handling for different
-      // exception types, but for now we'll just log the exception and
-      // return the message for printing.
+    // @TODO We may want to do different error handling for different
+    // exception types, but for now we'll just log the exception and
+    // return the message for printing.
     catch (Exception $e) {
       watchdog_exception('update', $e);
 
@@ -257,7 +254,7 @@ function update_invoke_post_update($function, &$context) {
       unset($variables['backtrace']);
       $ret['#abort'] = [
         'success' => FALSE,
-        'query' => t('%type: @message in %function (line %line of %file).', $variables)
+        'query' => t('%type: @message in %function (line %line of %file).', $variables),
       ];
     }
   }
diff --git a/core/lib/Drupal/Core/Extension/module.api.php b/core/lib/Drupal/Core/Extension/module.api.php
index 1b62360..5b3de7d 100644
--- a/core/lib/Drupal/Core/Extension/module.api.php
+++ b/core/lib/Drupal/Core/Extension/module.api.php
@@ -662,7 +662,7 @@ function hook_update_N(&$sandbox) {
 /**
  * Executes an update which is intended to update data, like entities.
  *
- * These implementations have to be placed in a $module.post_update.php file.
+ * These implementations have to be placed in a MODULE.post_update.php file.
  *
  * These updates are executed after all hook_update_N() implementations. At this
  * stage Drupal is already fully repaired so you can use any API as you wish.
@@ -679,12 +679,12 @@ function hook_update_N(&$sandbox) {
  *
  * @throws \Drupal\Core\Utility\UpdateException|PDOException
  *   In case of error, update hooks should throw an instance of
- *   Drupal\Core\Utility\UpdateException with a meaningful message for the user.
- *   If a database query fails for whatever reason, it will throw a
+ *   \Drupal\Core\Utility\UpdateException with a meaningful message for the
+ *   user. If a database query fails for whatever reason, it will throw a
  *   PDOException.
  *
  * @return string|null
- *   Optionally, post_update_Name hooks may return a translated string that will
+ *   Optionally, post_update_NAME() hooks may return a translated string that will
  *   be displayed to the user after the update has completed. If no message is
  *   returned, no message will be presented to the user.
  *
diff --git a/core/lib/Drupal/Core/Update/UpdateRegistry.php b/core/lib/Drupal/Core/Update/UpdateRegistry.php
index df662f2..1c4ade4 100644
--- a/core/lib/Drupal/Core/Update/UpdateRegistry.php
+++ b/core/lib/Drupal/Core/Update/UpdateRegistry.php
@@ -14,8 +14,8 @@
 /**
  * Provides all and missing hook_$updateName_NAME implementations.
  *
- * It therefore scans for functions in $module.$updateName.inc named like
- * $module_$updateName_NAME with NAME being a machine name.
+ * It therefore scans for functions in MODULE.$updateName.php named like
+ * MODULE_$updateName_NAME with NAME being a machine name.
  */
 class UpdateRegistry {
 
@@ -54,6 +54,27 @@ class UpdateRegistry {
    */
   protected $includeTests = NULL;
 
+  /**
+   * The site path.
+   *
+   * @var string
+   */
+  protected $sitePath;
+
+  /**
+   * Constructs a new UpdateRegistry.
+   *
+   * @param string $root
+   *   The app root.
+   * @param string $site_path
+   *   The site path.
+   * @param string[] $enabled_modules
+   *   A list of enabled modules.
+   * @param \Drupal\Core\KeyValueStore\KeyValueStoreInterface $key_value
+   *   The key value store.
+   * @param bool|NULL $include_tests
+   *   (optional) A flag whether to include tests in the scanning of modules.
+   */
   public function __construct($root, $site_path, array $enabled_modules, KeyValueStoreInterface $key_value, $include_tests = NULL) {
     $this->root = $root;
     $this->sitePath = $site_path;
@@ -66,6 +87,7 @@ public function __construct($root, $site_path, array $enabled_modules, KeyValueS
    * Gets all available update functions.
    *
    * @return callable[]
+   *   A list of update functions.
    */
   protected function getAvailableUpdateFunctions() {
     $regexp = '/^(?<module>.+)_' . $this->updateName . '_(?<name>.+)$/';
@@ -87,6 +109,7 @@ protected function getAvailableUpdateFunctions() {
    * Find all update functions that haven't been executed.
    *
    * @return callable[]
+   *   A list of update functions.
    */
   public function getPendingUpdateFunctions() {
     // We need a) the list of active modules (we get that from the config
@@ -95,7 +118,8 @@ public function getPendingUpdateFunctions() {
 
     $this->scanExtensionsAndLoadUpdateFiles();
 
-    // First figure out which hook_{$this->updateName}_NAME got executed already.
+    // First figure out which hook_{$this->updateName}_NAME got executed
+    // already.
     $existing_update_functions = $this->keyValue->get('existing_updates', []);
 
     $available_update_functions = $this->getAvailableUpdateFunctions();
@@ -166,12 +190,29 @@ public function getPendingUpdateInformation() {
   }
 
   /**
+   * Registers that a specific update got executed.
+   *
+   * @param string $function_name
+   *   The executed update function.
+   *
+   * @return $this
+   */
+  public function registerInvokedUpdate($function_name) {
+    $executed_updates = $this->keyValue->get('existing_updates', []);
+    $executed_updates[] = $function_name;
+    $this->keyValue->set('existing_updates', $executed_updates);
+
+    return $this;
+  }
+
+  /**
    * Returns all available updates for a given module.
    *
    * @param string $module_name
    *   The module name.
    *
    * @return callable[]
+   *   A list of update functions.
    */
   public function getModuleUpdateFunctions($module_name) {
     $this->scanExtensionsAndLoadUpdateFiles();
diff --git a/core/lib/Drupal/Core/Update/UpdateRegistryFactory.php b/core/lib/Drupal/Core/Update/UpdateRegistryFactory.php
new file mode 100644
index 0000000..0c076cb
--- /dev/null
+++ b/core/lib/Drupal/Core/Update/UpdateRegistryFactory.php
@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Update\UpdateRegistryFactory.
+ */
+
+namespace Drupal\Core\Update;
+
+use Symfony\Component\DependencyInjection\ContainerAwareInterface;
+use Symfony\Component\DependencyInjection\ContainerAwareTrait;
+
+/**
+ * Service factory for the update registry.
+ */
+class UpdateRegistryFactory implements ContainerAwareInterface {
+
+  use ContainerAwareTrait;
+
+  /**
+   * Creates a new UpdateRegistry instance.
+   *
+   * @return \Drupal\Core\Update\UpdateRegistry
+   *   The update registry instance.
+   */
+  public function configure() {
+    return new UpdateRegistry($this->container->get('app.root'), $this->container->get('site.path'), array_keys($this->container->get('module_handler')->getModuleList()), $this->container->get('keyvalue')->get('post_update'));
+  }
+
+}
diff --git a/core/modules/block/block.install b/core/modules/block/block.install
index a831fcb..f296e0d 100644
--- a/core/modules/block/block.install
+++ b/core/modules/block/block.install
@@ -96,5 +96,11 @@ function block_update_8001() {
 }
 
 /**
+ * Placeholder for the previous 8002 update.
+ */
+function block_update_8002() {
+}
+
+/**
  * @} End of "addtogroup updates-8.0.0-beta".
  */
diff --git a/core/modules/block/block.post_update.php b/core/modules/block/block.post_update.php
index f6cbbd5..f191ce2 100644
--- a/core/modules/block/block.post_update.php
+++ b/core/modules/block/block.post_update.php
@@ -14,6 +14,16 @@
  * Disable all blocks with missing context IDs in block_update_8001().
  */
 function block_post_update_disable_blocks_with_missing_contexts() {
+  // Don't execute the function if block_update_8002() got executed already,
+  // which used to do the same. Note: Its okay to check here, because
+  // update_do_one() does not update the installed schema version until the
+  // batch is finished.
+  $module_schema = drupal_get_installed_schema_version('block');
+
+  if ($module_schema == 8002) {
+    return;
+  }
+
   $block_update_8001 = \Drupal::keyValue('update_backup')->get('block_update_8001', []);
 
   $block_ids = array_keys($block_update_8001);
diff --git a/core/modules/system/src/Controller/DbUpdateController.php b/core/modules/system/src/Controller/DbUpdateController.php
index 0378f95..db0492b 100644
--- a/core/modules/system/src/Controller/DbUpdateController.php
+++ b/core/modules/system/src/Controller/DbUpdateController.php
@@ -76,6 +76,13 @@ class DbUpdateController extends ControllerBase {
   protected $root;
 
   /**
+   * The post update registry.
+   *
+   * @var \Drupal\Core\Update\UpdateRegistry
+   */
+  protected $postUpdateRegistry;
+
+  /**
    * Constructs a new UpdateController.
    *
    * @param string $root
@@ -92,8 +99,10 @@ class DbUpdateController extends ControllerBase {
    *   The current user.
    * @param \Drupal\Core\Render\BareHtmlPageRendererInterface $bare_html_page_renderer
    *   The bare HTML page renderer.
+   * @param \Drupal\Core\Update\UpdateRegistry $post_update_registry
+   *   The post update registry.
    */
-  public function __construct($root, KeyValueExpirableFactoryInterface $key_value_expirable_factory, CacheBackendInterface $cache, StateInterface $state, ModuleHandlerInterface $module_handler, AccountInterface $account, BareHtmlPageRendererInterface $bare_html_page_renderer) {
+  public function __construct($root, KeyValueExpirableFactoryInterface $key_value_expirable_factory, CacheBackendInterface $cache, StateInterface $state, ModuleHandlerInterface $module_handler, AccountInterface $account, BareHtmlPageRendererInterface $bare_html_page_renderer, UpdateRegistry $post_update_registry) {
     $this->root = $root;
     $this->keyValueExpirableFactory = $key_value_expirable_factory;
     $this->cache = $cache;
@@ -101,6 +110,7 @@ public function __construct($root, KeyValueExpirableFactoryInterface $key_value_
     $this->moduleHandler = $module_handler;
     $this->account = $account;
     $this->bareHtmlPageRenderer = $bare_html_page_renderer;
+    $this->postUpdateRegistry = $post_update_registry;
   }
 
   /**
@@ -114,7 +124,8 @@ public static function create(ContainerInterface $container) {
       $container->get('state'),
       $container->get('module_handler'),
       $container->get('current_user'),
-      $container->get('bare_html_page_renderer')
+      $container->get('bare_html_page_renderer'),
+      $container->get('update.post_update_registry')
     );
   }
 
@@ -260,14 +271,14 @@ protected function selection(Request $request) {
 
     $starting_updates = array();
     $incompatible_updates_exist = FALSE;
+    $updates_per_module = [];
     foreach (['update', 'post_update'] as $update_type) {
       switch ($update_type) {
         case 'update':
           $updates = update_get_update_list();
           break;
         case 'post_update':
-          $after_update_registry = $this->getPostUpdateRegistry();
-          $updates = $after_update_registry->getPendingUpdateInformation();
+          $updates = $this->postUpdateRegistry->getPendingUpdateInformation();
           break;
       }
       foreach ($updates as $module => $update) {
@@ -283,13 +294,17 @@ protected function selection(Request $request) {
           continue;
         }
         if (!empty($update['pending'])) {
+          $updates_per_module += [$module => []];
+          $updates_per_module[$module] = array_merge($updates_per_module[$module], $update['pending']);
           $build['start'][$module] = array(
             '#type' => 'hidden',
             '#value' => $update['start'],
           );
-          $build['start'][$module . '_' . $update_type] = array(
+          // Store the previous items in order to merge normal updates and
+          // post_update functions together.
+          $build['start'][$module] = array(
             '#theme' => 'item_list',
-            '#items' => $update['pending'],
+            '#items' => $updates_per_module[$module],
             '#title' => $module . ' module',
           );
 
@@ -589,8 +604,7 @@ protected function triggerBatch(Request $request) {
       }
     }
 
-    $post_update_registry = $this->getPostUpdateRegistry();
-    $post_updates = $post_update_registry->getPendingUpdateFunctions();
+    $post_updates = $this->postUpdateRegistry->getPendingUpdateFunctions();
 
     if ($post_updates) {
       // Now we rebuild all caches and after that execute the hook_post_update()
@@ -615,15 +629,6 @@ protected function triggerBatch(Request $request) {
   }
 
   /**
-   * Gets the update registry instance for the hook_post_update updates.
-   *
-   * @return \Drupal\Core\Update\UpdateRegistry
-   */
-  protected function getPostUpdateRegistry() {
-    return new UpdateRegistry($this->root, \Drupal::service('site.path'), array_keys($this->moduleHandler()->getModuleList()), \Drupal::keyValue('post_update'));
-  }
-
-  /**
    * Finishes the update process and stores the results for eventual display.
    *
    * After the updates run, all caches are flushed. The update results are
diff --git a/core/modules/system/src/Tests/Module/InstallTest.php b/core/modules/system/src/Tests/Module/InstallTest.php
index a1d6927..5f1a091 100644
--- a/core/modules/system/src/Tests/Module/InstallTest.php
+++ b/core/modules/system/src/Tests/Module/InstallTest.php
@@ -63,9 +63,11 @@ public function testRequiredModuleSchemaVersions() {
    * Ensures that post update functions are removed on uninstall.
    */
   public function testUninstallPostUpdateFunctions() {
+    \Drupal::service('module_installer')->uninstall(['module_test']);
+
     $post_update_key_value = \Drupal::keyValue('post_update');
     $existing_updates = $post_update_key_value->get('existing_updates', []);
-    $this->assertTrue(in_array('module_test_post_update_test', $existing_updates));
+    $this->assertFalse(in_array('module_test_post_update_test', $existing_updates));
   }
 
   /**
diff --git a/core/modules/system/src/Tests/Update/UpdatePostUpdateTest.php b/core/modules/system/src/Tests/Update/UpdatePostUpdateTest.php
index 4d3ac3d..7b84670 100644
--- a/core/modules/system/src/Tests/Update/UpdatePostUpdateTest.php
+++ b/core/modules/system/src/Tests/Update/UpdatePostUpdateTest.php
@@ -25,6 +25,17 @@ protected function setDatabaseDumpFiles() {
   }
 
   /**
+   * {@inheritdoc}
+   */
+  protected function doSelectionTest() {
+    parent::doSelectionTest();
+
+    // Ensure that normal and post_update updates are merged together on the
+    // selection page.
+    $this->assertRaw('<ul><li>8001 -   Normal update_N() function. </li><li>First update.</li><li>Second update.</li><li>Test1 update.</li><li>Test2 update.</li></ul>');
+  }
+
+  /**
    * Tests hook_post_update_NAME().
    */
   public function testPostUpdate() {
@@ -38,9 +49,12 @@ public function testPostUpdate() {
     ];
     $this->assertIdentical($updates, \Drupal::state()->get('post_update_test_execution', []));
 
-    $key_value = \Drupal::keyValue('update__post_update');
+    $key_value = \Drupal::keyValue('post_update');
     array_unshift($updates, 'block_post_update_disable_blocks_with_missing_contexts');
     $this->assertEqual($updates, $key_value->get('existing_updates'));
+
+    $this->drupalGet('update.php/selection');
+    $this->assertText('No pending updates.');
   }
 
 }
diff --git a/core/modules/system/tests/fixtures/update/drupal-8.update-test-postupdate-enabled.php b/core/modules/system/tests/fixtures/update/drupal-8.update-test-postupdate-enabled.php
index 1b2d186..375b50d 100644
--- a/core/modules/system/tests/fixtures/update/drupal-8.update-test-postupdate-enabled.php
+++ b/core/modules/system/tests/fixtures/update/drupal-8.update-test-postupdate-enabled.php
@@ -2,7 +2,8 @@
 
 /**
  * @file
- * Partial database to mimic the installation of the update_test_post_update module.
+ * Partial database to mimic the installation of the update_test_post_update
+ * module.
  */
 
 use Drupal\Core\Database\Database;
diff --git a/core/modules/system/tests/modules/update_test_postupdate/update_test_postupdate.install b/core/modules/system/tests/modules/update_test_postupdate/update_test_postupdate.install
new file mode 100644
index 0000000..f754d94
--- /dev/null
+++ b/core/modules/system/tests/modules/update_test_postupdate/update_test_postupdate.install
@@ -0,0 +1,7 @@
+<?php
+
+/**
+ * Normal update_N() function.
+ */
+function update_test_postupdate_update_8001() {
+}
diff --git a/core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php b/core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php
index 111655c..d740580 100644
--- a/core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php
+++ b/core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php
@@ -202,4 +202,38 @@ public function testGetModuleUpdateFunctions() {
     $this->assertEquals(['module_b_post_update_a'], array_values($update_registry->getModuleUpdateFunctions('module_b')));
   }
 
+  /**
+   * @covers ::registerInvokedUpdate
+   */
+  public function testRegisterInvokedUpdateWithoutExistingUpdates() {
+    $this->setupBasicModules();
+    $key_value = $this->prophesize(KeyValueStoreInterface::class);
+    $key_value->get('existing_updates', [])->willReturn([]);
+    $key_value->set('existing_updates', ['module_a_post_update_a'])->willReturn(NULL);
+    $key_value = $key_value->reveal();
+
+    $update_registry = new UpdateRegistry('vfs://drupal', 'sites/default', [
+      'module_a',
+      'module_b'
+    ], $key_value, FALSE);
+    $update_registry->registerInvokedUpdate('module_a_post_update_a');
+  }
+
+  /**
+   * @covers ::registerInvokedUpdate
+   */
+  public function testRegisterInvokedUpdateWithExistingUpdates() {
+    $this->setupBasicModules();
+    $key_value = $this->prophesize(KeyValueStoreInterface::class);
+    $key_value->get('existing_updates', [])->willReturn(['module_a_post_update_b']);
+    $key_value->set('existing_updates', ['module_a_post_update_b', 'module_a_post_update_a'])->willReturn(NULL);
+    $key_value = $key_value->reveal();
+
+    $update_registry = new UpdateRegistry('vfs://drupal', 'sites/default', [
+      'module_a',
+      'module_b'
+    ], $key_value, FALSE);
+    $update_registry->registerInvokedUpdate('module_a_post_update_a');
+  }
+
 }