diff --git a/core/lib/Drupal/Core/Entity/entity.api.php b/core/lib/Drupal/Core/Entity/entity.api.php
index 2b893fd..d65bab3 100644
--- a/core/lib/Drupal/Core/Entity/entity.api.php
+++ b/core/lib/Drupal/Core/Entity/entity.api.php
@@ -1817,7 +1817,7 @@
   // Add a property only to nodes of the 'article' bundle.
   if ($entity_type->id() == 'node' && $bundle == 'article') {
     $fields = [];
-    $fields['mymodule_text_more'] = BaseFieldDefinition::create('string')
+    $fields['mymodule_text_more'] = BundleFieldDefinition::create('string')
       ->setLabel(t('More text'))
       ->setComputed(TRUE)
       ->setClass('\Drupal\mymodule\EntityComputedMoreText');
diff --git a/core/lib/Drupal/Core/Field/BundleFieldDefinition.php b/core/lib/Drupal/Core/Field/BundleFieldDefinition.php
new file mode 100644
index 0000000..b06b47d
--- /dev/null
+++ b/core/lib/Drupal/Core/Field/BundleFieldDefinition.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace Drupal\Core\Field;
+
+use Drupal\Core\Field\BaseFieldDefinition;
+
+/**
+ * A class for defining bundle fields.
+ */
+class BundleFieldDefinition extends BaseFieldDefinition {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isBaseField() {
+    return FALSE;
+  }
+
+}