diff --git a/core/modules/migrate/src/Plugin/migrate/destination/Entity.php b/core/modules/migrate/src/Plugin/migrate/destination/Entity.php
index 8d69f80..60a2a0c 100644
--- a/core/modules/migrate/src/Plugin/migrate/destination/Entity.php
+++ b/core/modules/migrate/src/Plugin/migrate/destination/Entity.php
@@ -106,7 +106,7 @@ public function fields(MigrationInterface $migration = NULL) {
    *   The entity we're importing into.
    */
   protected function getEntity(Row $row, array $old_destination_id_values) {
-    $entity_id = $old_destination_id_values ? reset($old_destination_id_values) : $row->getDestinationProperty($this->getKey('id'));
+    $entity_id = $old_destination_id_values ? reset($old_destination_id_values) : $this->getEntityId($row);
     if (!empty($entity_id) && ($entity = $this->storage->load($entity_id))) {
       $this->updateEntity($entity, $row);
     }
@@ -126,6 +126,18 @@ protected function getEntity(Row $row, array $old_destination_id_values) {
   }
 
   /**
+   * Get the entity id of the row.
+   *
+   * @param \Drupal\migrate\Row $row
+   *   The row of data.
+   * @return string
+   *   The entity id for the row we're importing.
+   */
+  protected function getEntityId(Row $row) {
+    return $row->getDestinationProperty($this->getKey('id'));
+  }
+
+  /**
    * Returns a specific entity key.
    *
    * @param string $key
diff --git a/core/modules/migrate_drupal/src/Tests/d6/MigrateNodeBundleSettingsTest.php b/core/modules/migrate_drupal/src/Tests/d6/MigrateNodeBundleSettingsTest.php
index 38ceca1..503780c 100644
--- a/core/modules/migrate_drupal/src/Tests/d6/MigrateNodeBundleSettingsTest.php
+++ b/core/modules/migrate_drupal/src/Tests/d6/MigrateNodeBundleSettingsTest.php
@@ -44,6 +44,9 @@ public function setUp() {
     entity_create('node_type', array('type' => 'event'))->save();
     entity_create('node_type', array('type' => 'book'))->save();
 
+    // Create a config entity that already exists.
+    entity_create('base_field_override', array('field_name' => 'promote', 'entity_type' => 'node', 'bundle' => 'page',))->save();
+
     $id_mappings = array(
       'd6_node_type' => array(
         array(array('test_page'), array('test_page')),