diff --git a/core/modules/comment/tests/modules/comment_test/comment_test.module b/core/modules/comment/tests/modules/comment_test/comment_test.module
index 9fb600f..3f9f9a4 100644
--- a/core/modules/comment/tests/modules/comment_test/comment_test.module
+++ b/core/modules/comment/tests/modules/comment_test/comment_test.module
@@ -13,12 +13,22 @@
  * Implements hook_entity_type_alter().
  */
 function comment_test_entity_type_alter(array &$entity_types) {
+  static $invoked = FALSE;
+
   /** @var $entity_types \Drupal\Core\Entity\EntityTypeInterface[] */
-  if (\Drupal::languageManager()->isMultilingual()) {
-    // Enable language handling for comment fields.
-    $translation = $entity_types['comment']->get('translation');
-    $translation['comment_test'] = TRUE;
-    $entity_types['comment']->set('translation', $translation);
+  if (!$invoked) {
+    // Avoid infinite loops. ConfigurableLanguageManager::getLanguages()
+    // that isMultilingual() uses will use the entity API to load languages
+    // which will result in calling this hook again.
+    $invoked = TRUE;
+    if (\Drupal::languageManager()->isMultilingual()) {
+      // Allow further hook invocations to alter entities.
+      $invoked = FALSE;
+      // Enable language handling for comment fields.
+      $translation = $entity_types['comment']->get('translation');
+      $translation['comment_test'] = TRUE;
+      $entity_types['comment']->set('translation', $translation);
+    }
   }
 }