diff --git a/core/config/schema/core.data_types.schema.yml b/core/config/schema/core.data_types.schema.yml
index c695934..676b6ba 100644
--- a/core/config/schema/core.data_types.schema.yml
+++ b/core/config/schema/core.data_types.schema.yml
@@ -208,9 +208,8 @@ route:
           label: 'Param'
 
 # Config dependencies.
-config_dependencies:
+config_dependencies_calculated:
   type: mapping
-  label: 'Configuration dependencies'
   mapping:
     entity:
       type: sequence
@@ -228,6 +227,14 @@ config_dependencies:
       sequence:
         - type: string
 
+config_dependencies:
+  type: config_dependencies_calculated
+  label: 'Configuration dependencies'
+  mapping:
+    fixed:
+      type: config_dependencies_calculated
+      label: 'Fixed configuration dependencies'
+
 config_entity:
   type: mapping
   mapping:
diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
index d226243..44ef9f2 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
@@ -316,7 +316,14 @@ public function preSave(EntityStorageInterface $storage) {
   public function calculateDependencies() {
     // Dependencies should be recalculated on every save. This ensures stale
     // dependencies are never saved.
-    $this->dependencies = array();
+    if (isset($this->dependencies['fixed'])) {
+      $dependencies = $this->dependencies['fixed'];
+      $this->dependencies = $dependencies;
+      $this->dependencies['fixed'] = $dependencies;
+    }
+    else {
+      $this->dependencies = array();
+    }
     if ($this instanceof EntityWithPluginBagsInterface) {
       // Configuration entities need to depend on the providers of any plugins
       // that they store the configuration for.
diff --git a/core/modules/block/src/Tests/BlockConfigSchemaTest.php b/core/modules/block/src/Tests/BlockConfigSchemaTest.php
index 47e2421..ccd0a73 100644
--- a/core/modules/block/src/Tests/BlockConfigSchemaTest.php
+++ b/core/modules/block/src/Tests/BlockConfigSchemaTest.php
@@ -36,6 +36,7 @@ class BlockConfigSchemaTest extends KernelTestBase {
     'system',
     'taxonomy',
     'user',
+    'text',
   );
 
   /**
@@ -61,6 +62,8 @@ protected function setUp() {
     $this->typedConfig = \Drupal::service('config.typed');
     $this->blockManager = \Drupal::service('plugin.manager.block');
     $this->installEntitySchema('block_content');
+    $this->installEntitySchema('taxonomy_term');
+    $this->installEntitySchema('node');
   }
 
   /**
diff --git a/core/modules/comment/src/Tests/CommentFieldsTest.php b/core/modules/comment/src/Tests/CommentFieldsTest.php
index a0cb95d..017f3fb 100644
--- a/core/modules/comment/src/Tests/CommentFieldsTest.php
+++ b/core/modules/comment/src/Tests/CommentFieldsTest.php
@@ -63,6 +63,29 @@ function testCommentDefaultFields() {
   }
 
   /**
+   * Tests that you can remove a comment field.
+   */
+  public function testCommentFieldDelete() {
+    $this->drupalCreateContentType(array('type' => 'test_node_type'));
+    $this->container->get('comment.manager')->addDefaultField('node', 'test_node_type');
+    // We want to test the handling of removing the primary comment field, so we
+    // ensure there is at least one other comment field attached to a node type
+    // so that comment_entity_load() runs for nodes.
+    $this->container->get('comment.manager')->addDefaultField('node', 'test_node_type', 'comment2');
+
+    // Create a sample node.
+    $node = $this->drupalCreateNode(array(
+      'title' => 'Baloney',
+      'type' => 'test_node_type',
+    ));
+
+    // Delete the first comment field.
+    FieldStorageConfig::loadByName('node', 'comment')->delete();
+    $this->drupalGet('node/' . $node->nid->value);
+    $this->assertResponse(200);
+  }
+
+  /**
    * Tests that comment module works when installed after a content module.
    */
   function testCommentInstallAfterContentModule() {
diff --git a/core/modules/config/src/Tests/ConfigImportAllTest.php b/core/modules/config/src/Tests/ConfigImportAllTest.php
index 7b73631..bc801c3 100644
--- a/core/modules/config/src/Tests/ConfigImportAllTest.php
+++ b/core/modules/config/src/Tests/ConfigImportAllTest.php
@@ -76,8 +76,16 @@ public function testInstallUninstall() {
     // Purge the data.
     field_purge_batch(1000);
 
+    // Delete any forum terms so it can be uninstalled.
+    $vid = \Drupal::config('forum.settings')->get('vocabulary');
+    $terms = entity_load_multiple_by_properties('taxonomy_term', ['vid' => $vid]);
+    foreach ($terms as $term) {
+      $term->delete();
+    }
+
     system_list_reset();
     $all_modules = system_rebuild_module_data();
+
     $modules_to_uninstall = array_filter($all_modules, function ($module) {
       // Filter required and not enabled modules.
       if (!empty($module->info['required']) || $module->status == FALSE) {
diff --git a/core/modules/forum/config/install/node.type.forum.yml b/core/modules/forum/config/install/node.type.forum.yml
index f7833f7..a3dccc4 100644
--- a/core/modules/forum/config/install/node.type.forum.yml
+++ b/core/modules/forum/config/install/node.type.forum.yml
@@ -1,9 +1,13 @@
-type: forum
+langcode: en
+status: true
+dependencies:
+  fixed:
+    module:
+      - forum
 name: 'Forum topic'
+type: forum
 description: 'A <em>forum topic</em> starts a new discussion thread within a forum.'
 help: ''
 new_revision: false
-display_submitted: true
 preview_mode: 1
-status: true
-langcode: en
+display_submitted: true
diff --git a/core/modules/forum/forum.module b/core/modules/forum/forum.module
index b744c0f..6f942c5 100644
--- a/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -11,8 +11,11 @@
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Url;
 use Drupal\Component\Utility\String;
+use Drupal\Core\Extension\Extension;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\taxonomy\Entity\Vocabulary;
+use Symfony\Component\Routing\Exception\RouteNotFoundException;
 
 /**
  * Implements hook_help().
@@ -690,3 +693,63 @@ function template_preprocess_forum_submitted(&$variables) {
   }
   $variables['time'] = isset($variables['topic']->created) ? \Drupal::service('date.formatter')->formatInterval(REQUEST_TIME - $variables['topic']->created) : '';
 }
+
+/**
+ * Implements hook_system_info_alter().
+ *
+ * Prevents forum module from being uninstalled whilst any forum nodes exist
+ * or there are any terms in the forum vocabulary.
+ */
+function forum_system_info_alter(&$info, Extension $file, $type) {
+  // It is not safe use the entity query service during maintenance mode.
+  if ($type == 'module' && !defined('MAINTENANCE_MODE') && $file->getName() == 'forum') {
+    $factory = \Drupal::service('entity.query');
+    $nodes = $factory->get('node')
+      ->condition('type', 'forum')
+      ->accessCheck(FALSE)
+      ->range(0, 1)
+      ->execute();
+    if (!empty($nodes)) {
+      $info['required'] = TRUE;
+      $info['explanation'] = t('To uninstall Forum first delete all <em>Forum</em> content.');
+    }
+    $vid = \Drupal::config('forum.settings')->get('vocabulary');
+    $terms = $factory->get('taxonomy_term')
+      ->condition('vid', $vid)
+      ->accessCheck(FALSE)
+      ->range(0, 1)
+      ->execute();
+    if (!empty($terms)) {
+      $vocabulary = Vocabulary::load($vid);
+      $info['required'] = TRUE;
+      try {
+        if (!empty($info['explanation'])) {
+          if ($vocabulary->access('view')) {
+            $info['explanation'] = t('To uninstall Forum first delete all <em>Forum</em> content and <a href="!url">%vocabulary</a> terms.', [
+              '%vocabulary' => $vocabulary->label(),
+              '!url' => $vocabulary->url('overview-form'),
+            ]);
+          }
+          else {
+            $info['explanation'] = t('To uninstall Forum first delete all <em>Forum</em> content and %vocabulary terms.', [
+              '%vocabulary' => $vocabulary->label()
+            ]);
+          }
+        }
+        else {
+          $info['explanation'] = t('To uninstall Forum first delete all <a href="!url">%vocabulary</a> terms.', [
+            '%vocabulary' => $vocabulary->label(),
+            '!url' => $vocabulary->url('overview-form'),
+          ]);
+        }
+      }
+      catch (RouteNotFoundException $e) {
+        // Route rebuilding might not have occurred before this hook is fired.
+        // Just use an explanation without a link for the time being.
+        $info['explanation'] = t('To uninstall Forum first delete all <em>Forum</em> content and %vocabulary terms.', [
+          '%vocabulary' => $vocabulary->label()
+        ]);
+      }
+    }
+  }
+}
diff --git a/core/modules/forum/src/Tests/ForumUninstallTest.php b/core/modules/forum/src/Tests/ForumUninstallTest.php
index 388910c..2c2e89e 100644
--- a/core/modules/forum/src/Tests/ForumUninstallTest.php
+++ b/core/modules/forum/src/Tests/ForumUninstallTest.php
@@ -9,7 +9,12 @@
 
 use Drupal\comment\CommentInterface;
 use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\Component\Utility\String;
+use Drupal\Core\DrupalKernel;
+use Drupal\Core\Session\UserSession;
+use Drupal\Core\Site\Settings;
 use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\node\Entity\NodeType;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -29,7 +34,8 @@ class ForumUninstallTest extends WebTestBase {
   /**
    * Tests if forum module uninstallation properly deletes the field.
    */
-  function testForumUninstallWithField() {
+  public function testForumUninstallWithField() {
+    $this->drupalLogin($this->drupalCreateUser(['administer taxonomy', 'administer nodes', 'administer modules', 'delete any forum content', 'administer content types']));
     // Ensure that the field exists before uninstallation.
     $field_storage = FieldStorageConfig::loadByName('node', 'taxonomy_forums');
     $this->assertNotNull($field_storage, 'The taxonomy_forums field storage exists.');
@@ -65,27 +71,69 @@ function testForumUninstallWithField() {
     ));
     $comment->save();
 
-    // Uninstall the forum module which should trigger field deletion.
-    $this->container->get('module_handler')->uninstall(array('forum'));
-
-    // We want to test the handling of removing the forum comment field, so we
-    // ensure there is at least one other comment field attached to a node type
-    // so that comment_entity_load() runs for nodes.
-    \Drupal::service('comment.manager')->addDefaultField('node', 'forum', 'another_comment_field', CommentItemInterface::OPEN, 'another_comment_field');
-
-    $this->drupalGet('node/' . $node->nid->value);
-    $this->assertResponse(200);
+    // Attempt to uninstall forum.
+    $this->drupalGet('admin/modules/uninstall');
+    // Assert forum is required.
+    $this->assertNoFieldByName('uninstall[forum]');
+    $this->drupalGet('admin/modules');
+    $this->assertText('To uninstall Forum first delete all Forum content');
+
+    // Delete the node.
+    $this->drupalPostForm('node/' . $node->id() . '/delete', array(), t('Delete'));
+
+    // Attempt to uninstall forum.
+    $this->drupalGet('admin/modules/uninstall');
+    // Assert forum is still required.
+    $this->assertNoFieldByName('uninstall[forum]');
+    $this->drupalGet('admin/modules');
+    $this->assertText('To uninstall Forum first delete all Forums terms');
+
+    // Delete any forum terms.
+    $vid = \Drupal::config('forum.settings')->get('vocabulary');
+    $terms = entity_load_multiple_by_properties('taxonomy_term', ['vid' => $vid]);
+    foreach ($terms as $term) {
+      $term->delete();
+    }
+
+    // Ensure that the forum node type can not be deleted.
+    $this->drupalGet('admin/structure/types/manage/forum');
+    $this->assertNoLink(t('Delete'));
+
+    // Now attempt to uninstall forum.
+    $this->drupalGet('admin/modules/uninstall');
+    // Assert forum is no longer required.
+    $this->assertFieldByName('uninstall[forum]');
+    $this->drupalGet('admin/modules');
+    $this->assertNoText('To uninstall Forum first delete all Forum content');
+    $this->drupalPostForm('admin/modules/uninstall', array(
+      'uninstall[forum]' => 1,
+    ), t('Uninstall'));
+    $this->drupalPostForm(NULL, [], t('Uninstall'));
 
     // Check that the field is now deleted.
     $field_storage = FieldStorageConfig::loadByName('node', 'taxonomy_forums');
     $this->assertNull($field_storage, 'The taxonomy_forums field storage has been deleted.');
-  }
 
+    // Check that a node type with a machine name of forum can be created after
+    // uninstalling the forum module and the node type is not locked.
+    $edit = array(
+      'name' => 'Forum',
+      'title_label' => 'title for forum',
+      'type' => 'forum',
+    );
+    $this->drupalPostForm('admin/structure/types/add', $edit, t('Save content type'));
+    $this->assertTrue((bool) NodeType::load('forum'), 'Node type with machine forum created.');
+    $this->drupalGet('admin/structure/types/manage/forum');
+    $this->clickLink(t('Delete'));
+    $this->drupalPostForm(NULL, array(), t('Delete'));
+    $this->assertResponse(200);
+    $this->assertFalse((bool) NodeType::load('forum'), 'Node type with machine forum deleted.');
+  }
 
   /**
    * Tests uninstallation if the field storage has been deleted beforehand.
    */
-  function testForumUninstallWithoutFieldStorage() {
+  public function testForumUninstallWithoutFieldStorage() {
     // Manually delete the taxonomy_forums field before module uninstallation.
     $field_storage = FieldStorageConfig::loadByName('node', 'taxonomy_forums');
     $this->assertNotNull($field_storage, 'The taxonomy_forums field storage exists.');
diff --git a/core/modules/node/src/Tests/NodeTypePersistenceTest.php b/core/modules/node/src/Tests/NodeTypePersistenceTest.php
deleted file mode 100644
index 62c2783..0000000
--- a/core/modules/node/src/Tests/NodeTypePersistenceTest.php
+++ /dev/null
@@ -1,62 +0,0 @@
-<?php
-
-/**
- * @file
- * Definition of Drupal\node\Tests\NodeTypePersistenceTest.
- */
-
-namespace Drupal\node\Tests;
-
-/**
- * Ensures that node type customization survives module enabling and disabling.
- *
- * @group node
- */
-class NodeTypePersistenceTest extends NodeTestBase {
-  // Enable the prerequisite modules for forum
-  public static $modules = array('history', 'taxonomy', 'options', 'comment');
-  /**
-   * Tests that node type customizations persist through disable and uninstall.
-   */
-  function testNodeTypeCustomizationPersistence() {
-    $web_user = $this->drupalCreateUser(array('bypass node access', 'administer content types', 'administer modules'));
-    $this->drupalLogin($web_user);
-    $forum_key = 'modules[Core][forum][enable]';
-    $forum_enable = array($forum_key => "1");
-
-    // Enable forum and verify that the node type exists and is not disabled.
-    $this->drupalPostForm('admin/modules', $forum_enable, t('Save configuration'));
-    $forum = entity_load('node_type', 'forum');
-    $this->assertTrue($forum->id(), 'Forum node type found.');
-    $this->assertTrue($forum->isLocked(), 'Forum node type is locked');
-
-    // Check that forum node type (uncustomized) shows up.
-    $this->drupalGet('node/add');
-    $this->assertText('forum', 'forum type is found on node/add');
-
-    // Customize forum description.
-    $description = $this->randomMachineName();
-    $edit = array('description' => $description);
-    $this->drupalPostForm('admin/structure/types/manage/forum', $edit, t('Save content type'));
-
-    // Check that forum node type customization shows up.
-    $this->drupalGet('node/add');
-    $this->assertText($description, 'Customized description found');
-
-    // Uninstall forum.
-    $edit = array('uninstall[forum]' => 'forum');
-    $this->drupalPostForm('admin/modules/uninstall', $edit, t('Uninstall'));
-    $this->drupalPostForm(NULL, array(), t('Uninstall'));
-    $forum = entity_load('node_type', 'forum');
-    $this->assertFalse($forum->isLocked(), 'Forum node type is not locked');
-    $this->drupalGet('node/add');
-    $this->assertNoText('forum', 'forum type is no longer found on node/add');
-
-    // Reenable forum and check that the customization survived the module
-    // uninstall.
-    $this->drupalPostForm('admin/modules', $forum_enable, t('Save configuration'));
-    $this->drupalGet('node/add');
-    $this->assertText($description, 'Customized description is found even after uninstall and reenable.');
-  }
-
-}
diff --git a/core/modules/node/src/Tests/NodeTypeTest.php b/core/modules/node/src/Tests/NodeTypeTest.php
index b0bb658..7b7c50a 100644
--- a/core/modules/node/src/Tests/NodeTypeTest.php
+++ b/core/modules/node/src/Tests/NodeTypeTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\node\Tests;
 use Drupal\field\Entity\FieldConfig;
+use Drupal\node\Entity\NodeType;
 
 /**
  * Ensures that node type functions work correctly.
@@ -183,20 +184,28 @@ function testNodeTypeDeletion() {
       'The content type is available for deletion.'
     );
     $this->assertText(t('This action cannot be undone.'), 'The node type deletion confirmation form is available.');
-    // Test that forum node type could not be deleted while forum active.
-    $this->container->get('module_handler')->install(array('forum'));
+
+    // Test that a locked node type could not be deleted.
+    $this->container->get('module_handler')->install(array('node_test_config'));
+    // Lock the default node type.
+    $locked = \Drupal::state()->get('node.type.locked');
+    $locked['default'] = 'default';
+    \Drupal::state()->set('node.type.locked', $locked);
     // Call to flush all caches after installing the forum module in the same
     // way installing a module through the UI does.
     $this->resetAll();
-    $this->drupalGet('admin/structure/types/manage/forum');
+    $this->drupalGet('admin/structure/types/manage/default');
     $this->assertNoLink(t('Delete'));
-    $this->drupalGet('admin/structure/types/manage/forum/delete');
+    $this->drupalGet('admin/structure/types/manage/default/delete');
     $this->assertResponse(403);
-    $this->container->get('module_handler')->uninstall(array('forum'));
-    $this->drupalGet('admin/structure/types/manage/forum');
-    $this->assertLink(t('Delete'));
-    $this->drupalGet('admin/structure/types/manage/forum/delete');
+    $this->container->get('module_handler')->uninstall(array('node_test_config'));
+    unset($locked['default']);
+    \Drupal::state()->set('node.type.locked', $locked);
+    $this->drupalGet('admin/structure/types/manage/default');
+    $this->clickLink(t('Delete'));
     $this->assertResponse(200);
+    $this->drupalPostForm(NULL, array(), t('Delete'));
+    $this->assertFalse((bool) NodeType::load('default'), 'Node type with machine default deleted.');
   }
 
   /**
diff --git a/core/modules/system/src/Tests/Module/DependencyTest.php b/core/modules/system/src/Tests/Module/DependencyTest.php
index 6ef1fb9..710341c 100644
--- a/core/modules/system/src/Tests/Module/DependencyTest.php
+++ b/core/modules/system/src/Tests/Module/DependencyTest.php
@@ -154,6 +154,15 @@ function testUninstallDependents() {
     $checkbox = $this->xpath('//input[@type="checkbox" and @name="uninstall[comment]"]');
     $this->assert(count($checkbox) == 0, 'Checkbox for uninstalling the comment module not found.');
 
+    // Delete any forum terms.
+    $vid = \Drupal::config('forum.settings')->get('vocabulary');
+    // Ensure taxonomy has been loaded into the test-runner after forum was
+    // enabled.
+    \Drupal::moduleHandler()->load('taxonomy');
+    $terms = entity_load_multiple_by_properties('taxonomy_term', ['vid' => $vid]);
+    foreach ($terms as $term) {
+      $term->delete();
+    }
     // Uninstall the forum module, and check that taxonomy now can also be
     // uninstalled.
     $edit = array('uninstall[forum]' => 'forum');
diff --git a/core/modules/system/src/Tests/Module/InstallUninstallTest.php b/core/modules/system/src/Tests/Module/InstallUninstallTest.php
index c826d1c..4005ee1 100644
--- a/core/modules/system/src/Tests/Module/InstallUninstallTest.php
+++ b/core/modules/system/src/Tests/Module/InstallUninstallTest.php
@@ -14,7 +14,7 @@
  */
 class InstallUninstallTest extends ModuleTestBase {
 
-  public static $modules = array('system_test', 'dblog');
+  public static $modules = array('system_test', 'dblog', 'taxonomy');
 
   /**
    * Tests that a fixed set of modules can be installed and uninstalled.
@@ -151,6 +151,15 @@ public function testInstallUninstall() {
    */
   protected function assertSuccessfullUninstall($module, $package = 'Core') {
     $edit = array();
+    if ($module == 'forum') {
+      // Forum cannot be uninstalled until all of the content entities related
+      // to it have been deleted.
+      $vid = \Drupal::config('forum.settings')->get('vocabulary');
+      $terms = entity_load_multiple_by_properties('taxonomy_term', ['vid' => $vid]);
+      foreach ($terms as $term) {
+        $term->delete();
+      }
+    }
     $edit['uninstall[' . $module . ']'] = TRUE;
     $this->drupalPostForm('admin/modules/uninstall', $edit, t('Uninstall'));
     $this->drupalPostForm(NULL, NULL, t('Uninstall'));