diff -u b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
--- b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
+++ b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
@@ -13,7 +13,6 @@
 use Drupal\Core\State\StateInterface;
 use Drupal\migrate\Entity\MigrationInterface;
 use Drupal\migrate\MigrateException;
-use Drupal\migrate\MigrateSkipRowException;
 use Drupal\migrate\Plugin\migrate\destination\EntityContentBase;
 use Drupal\migrate\Row;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -40,7 +39,7 @@
   protected $entityQuery;
 
   /**
-   * An array of entity Ids for the 'commented entity' keyed by entity type.
+   * An array of entity IDs for the 'commented entity' keyed by entity type.
    *
    * @var array
    */
@@ -119,19 +118,18 @@
     if (empty($this->stubCommentedEntityIds[$stub_commented_entity_type])) {
       // Fill stub entity id. Any id will do, as long as it exists.
       $entity_type = $this->entityManager->getDefinition($stub_commented_entity_type);
-      if ($id_key = $entity_type->getKey('id')) {
-        $result = $this->entityQuery
-          ->get($stub_commented_entity_type)
-          ->range(0, 1)
-          ->execute();
-        if ($result) {
-          $this->stubCommentedEntityIds[$stub_commented_entity_type] = array_pop($result);
-          $row->setSourceProperty($id_key, $this->stubCommentedEntityIds[$stub_commented_entity_type]);
-        }
+      $id_key = $entity_type->getKey('id');
+      $result = $this->entityQuery
+        ->get($stub_commented_entity_type)
+        ->range(0, 1)
+        ->execute();
+      if ($result) {
+        $this->stubCommentedEntityIds[$stub_commented_entity_type] = array_pop($result);
+        $row->setSourceProperty($id_key, $this->stubCommentedEntityIds[$stub_commented_entity_type]);
+      }
+      else {
+        throw new MigrateException(t('Could not find parent entity to use for comment %id', ['%id' => implode(':', $row->getSourceIdValues())]), MigrationInterface::MESSAGE_ERROR);
       }
-    }
-    if (empty($this->stubCommentedEntityIds[$stub_commented_entity_type])) {
-      throw new MigrateException(t('Could not derive commented entity for comment %id', ['%id' => implode(':', $row->getSourceIdValues())]), MigrationInterface::MESSAGE_ERROR);
     }
 
     $row->setDestinationProperty('entity_id', $this->stubCommentedEntityIds[$stub_commented_entity_type]);
diff -u b/core/modules/comment/src/Tests/Migrate/d6/MigrateCommentTest.php b/core/modules/comment/src/Tests/Migrate/d6/MigrateCommentTest.php
--- b/core/modules/comment/src/Tests/Migrate/d6/MigrateCommentTest.php
+++ b/core/modules/comment/src/Tests/Migrate/d6/MigrateCommentTest.php
@@ -20,8 +20,8 @@
   use CommentTestTrait;
 
   // Directly testing that comments' entity_id is populated upon importing is
-  // not straightforward, but RDF module serves as an implicit test;
-  // its hook_comment_storage_load() references $comment->getCommentedEntity().
+  // not straightforward, but RDF module serves as an implicit test -
+  // its hook_comment_storage_load() references a stubbed comment.
   static $modules = ['node', 'comment', 'text', 'filter', 'rdf'];
 
   /**