diff -u b/email_registration.module b/email_registration.module
--- b/email_registration.module
+++ b/email_registration.module
@@ -45,7 +45,12 @@
   // Ensure whatever name we have is unique.
   $new_name = email_registration_unique_username($new_name, $account->id());
 
-  $account->setUsername($new_name)->save();
+  $account->setUsername($new_name);
+  if ($account->isValidationRequired() && !$account->validate()) {
+    \Drupal::logger('email_registration')->error('Email registration failed setting the new name on user @id.', ['@id' => $account->id()]);
+    return;
+  }
+  $account->save();
 }
 
 /**