diff --git a/src/Form/GatsbyAdminForm.php b/src/Form/GatsbyAdminForm.php
index 9958edc..25432d5 100644
--- a/src/Form/GatsbyAdminForm.php
+++ b/src/Form/GatsbyAdminForm.php
@@ -76,7 +76,7 @@ class GatsbyAdminForm extends ConfigFormBase {
     $form['preview_entity_types'] = [
       '#type' => 'checkboxes',
       '#options' => $this->getContentEntityTypes(),
-      '#default_value' => $config->get('preview_entity_types'),
+      '#default_value' => $config->get('preview_entity_types') ?: [],
       '#title' => $this->t('Entity types to send to Gatsby Preview Server'),
       '#description' => $this->t('What entities should be sent to the Gatsby Preview Server?'),
     ];