diff --git a/core/modules/comment/comment.install b/core/modules/comment/comment.install
index 8822f4b..0331d63 100644
--- a/core/modules/comment/comment.install
+++ b/core/modules/comment/comment.install
@@ -6,6 +6,7 @@
  */
 
 use Drupal\Core\Language\Language;
+use Drupal\comment\Plugin\field\field_type\CommentItem;
 
 /**
  * Implements hook_uninstall().
@@ -586,6 +587,15 @@ function comment_update_8006(&$sandbox) {
       // Increment index.
       $index++;
     }
+    // Comment module may be disabled so we will need to inject the schema to
+    // avoid attempting to create a Field of an unknown type.
+    if (!Drupal::moduleHandler()->moduleExists('comment')) {
+      // We can't use the autoloader because the comment namespace isn't
+      // registered.
+      // @todo Remove once https://drupal.org/node/1199946 is in.
+      require_once __DIR__ . '/lib/Drupal/comment/Plugin/field/field_type/CommentItem.php';
+      $field['schema'] = CommentItem::schema();
+    }
     _update_8003_field_create_field($field);
 
     if (Drupal::config("field.instance.node.$node_type." . $field['id'])->isNew()) {
diff --git a/core/modules/comment/lib/Drupal/comment/Plugin/field/field_type/CommentItem.php b/core/modules/comment/lib/Drupal/comment/Plugin/field/field_type/CommentItem.php
index 6f9ad12..b3ac601 100644
--- a/core/modules/comment/lib/Drupal/comment/Plugin/field/field_type/CommentItem.php
+++ b/core/modules/comment/lib/Drupal/comment/Plugin/field/field_type/CommentItem.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Entity\Annotation\FieldType;
+use Drupal\Core\Entity\Field\PrepareCacheInterface;
 use Drupal\field\Plugin\Core\Entity\Field;
 use Drupal\field\Plugin\Type\FieldType\ConfigFieldItemBase;
 
@@ -32,7 +33,7 @@
  *   default_formatter = "comment_default"
  * )
  */
-class CommentItem extends ConfigFieldItemBase {
+class CommentItem extends ConfigFieldItemBase implements PrepareCacheInterface {
 
   /**
    * Definitions of the contained properties.
@@ -58,7 +59,7 @@ public function getPropertyDefinitions() {
   /**
    * {@inheritdoc}
    */
-  public static function schema(Field $field) {
+  public static function schema(Field $field = NULL) {
     return array(
       'columns' => array(
         'status' => array(
@@ -160,4 +161,9 @@ public function isEmpty() {
     return FALSE;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function prepareCache() {}
+
 }
diff --git a/core/modules/comment/lib/Drupal/comment/Tests/CommentFieldsTest.php b/core/modules/comment/lib/Drupal/comment/Tests/CommentFieldsTest.php
index 96c5e6f..a4020f7 100644
--- a/core/modules/comment/lib/Drupal/comment/Tests/CommentFieldsTest.php
+++ b/core/modules/comment/lib/Drupal/comment/Tests/CommentFieldsTest.php
@@ -69,8 +69,16 @@ function testCommentEnable() {
 
     // Drop default comment field added in CommentTestBase::setup().
     entity_load('field_entity', 'comment')->delete();
-    $this->cronRun();
-    $this->cronRun();
+    if ($field = field_info_field('comment_node_forum')) {
+      $field->delete();
+    }
+
+    // Purge field data now to allow comment module to be disabled once the
+    // field has been deleted.
+    field_purge_batch(10);
+    // Call again as field_purge_batch() won't remove both the instances and
+    // field in a single pass.
+    field_purge_batch(10);
 
     // Disable the comment module.
     $edit = array();
diff --git a/core/modules/system/lib/Drupal/system/Tests/Module/DependencyTest.php b/core/modules/system/lib/Drupal/system/Tests/Module/DependencyTest.php
index eb98602..44ed59a 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Module/DependencyTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Module/DependencyTest.php
@@ -190,10 +190,7 @@ function testUninstallDependents() {
     $this->drupalPost('admin/modules/uninstall', $edit, t('Uninstall'));
     $this->drupalPost(NULL, NULL, t('Uninstall'));
     $this->assertText(t('The selected modules have been uninstalled.'), 'Modules status has been updated.');
-    // Delete comment field to allow disabling of the comment module.
-    entity_load('field_entity', 'comment_node_forum')->delete();
-    // Purge comment field storage data.
-    field_purge_batch(10);
+
     // Disable the comment module.
     $edit = array('modules[Core][comment][enable]' => FALSE);
     $this->drupalPost('admin/modules', $edit, t('Save configuration'));