diff --git a/core/modules/comment/lib/Drupal/comment/CommentStorageController.php b/core/modules/comment/lib/Drupal/comment/CommentStorageController.php
index 60eb5ff..3298657 100644
--- a/core/modules/comment/lib/Drupal/comment/CommentStorageController.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentStorageController.php
@@ -291,6 +291,8 @@ public function baseFieldDefinitions() {
       'label' => t('Entity ID'),
       'description' => t('The ID of the entity of which this comment is a reply.'),
       'type' => 'entity_reference_field',
+      // @todo Implement a 'class' to get referenced entity at runtime.
+      'class' => '\Drupal\comment\Type\CommentEntityItem',
       'settings' => array('target_type' => 'node'),
       'required' => TRUE,
     );
diff --git a/core/modules/comment/lib/Drupal/comment/Type/CommentEntityItem.php b/core/modules/comment/lib/Drupal/comment/Type/CommentEntityItem.php
new file mode 100644
index 0000000..16062a2
--- /dev/null
+++ b/core/modules/comment/lib/Drupal/comment/Type/CommentEntityItem.php
@@ -0,0 +1,58 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\comment\Type\CommentEntityItem.
+ */
+
+namespace Drupal\comment\Type;
+
+use Drupal\Core\Entity\Field\FieldItemBase;
+use Drupal\entity_reference\Type\ConfigurableEntityReferenceItem;
+
+/**
+ * Defines the 'commented entity' field item.
+ */
+class CommentEntityItem extends ConfigurableEntityReferenceItem {
+
+  /**
+   * Property definitions of the contained properties.
+   *
+   * @see CommentEntityItem::getPropertyDefinitions()
+   *
+   * @var array
+   */
+  static $propertyDefinitions;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPropertyDefinitions() {
+
+    if (!isset(static::$propertyDefinitions)) {
+      // @todo find a entity the comment attached to.
+      $entity_type = 'node';
+      static::$propertyDefinitions['entity_id'] = array(
+        'type' => 'entity_reference',
+        'settings' => array('target_type' => $entity_type),
+      );
+    }
+    return static::$propertyDefinitions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getValue($langcode = NULL) {
+    if (!isset($this->value)) {
+      if (!isset($this->parent)) {
+        throw new InvalidArgumentException('Computed properties require context for computation.');
+      }
+      $field = $this->parent->getParent();
+      $entity = $field->getParent();
+      $this->value = $entity;
+    }
+    return $this->value;
+  }
+
+}