diff --git a/src/Plugin/MediaEntity/Type/Twitter.php b/src/Plugin/MediaEntity/Type/Twitter.php
index 97defcf..9d7d2dc 100644
--- a/src/Plugin/MediaEntity/Type/Twitter.php
+++ b/src/Plugin/MediaEntity/Type/Twitter.php
@@ -245,7 +245,7 @@ class Twitter extends MediaTypeBase {
    * {@inheritdoc}
    */
   public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
-    $options = [];
+    $options = ['' => $this->t('- None -')];
     $allowed_field_types = ['string', 'string_long', 'link'];
     /** @var \Drupal\media_entity\MediaBundleInterface $bundle */
     $bundle = $form_state->getFormObject()->getEntity();
@@ -255,24 +255,25 @@ class Twitter extends MediaTypeBase {
       }
     }
 
+    // Select the source field. Only show when the bundle is not new, so there
+    // will potentially be fields to select.
     $form['source_field'] = array(
       '#type' => 'select',
       '#title' => $this->t('Field with source information'),
       '#description' => $this->t('Field on media entity that stores Twitter embed code or URL. You can create a bundle without selecting a value for this dropdown initially. This dropdown can be populated after adding fields to the bundle.'),
       '#default_value' => empty($this->configuration['source_field']) ? static::MEDIA_ENTITY_TWITTER_DEFAULT_FIELD_NAME : $this->configuration['source_field'],
       '#options' => $options,
+      '#access' => !$bundle->isNew(),
     );
 
     // Add a checkbox to allow the field being created automatically on save.
-    if (empty($this->configuration['source_field'])) {
-      $form['create_source_field'] = [
-        '#type' => 'checkbox',
-        '#title' => $this->t('Create a source field automatically when saving this form.'),
-        '#description' => $this->t('If checked, a default field will be created and used as a source field. You can change this setting later.'),
-        '#default_value' => $this->configuration['create_source_field'],
-        '#access' => $bundle->isNew(),
-      ];
-    }
+    $form['create_source_field'] = [
+      '#type' => 'checkbox',
+      '#title' => $this->t('Create a source field automatically when saving this form.'),
+      '#description' => $this->t('If checked, a default field will be created and used as a source field. If you uncheck the field, you will need to create a field and revisit this form later to select it.'),
+      '#default_value' => TRUE,
+      '#access' => $bundle->isNew(),
+    ];
 
     $form['use_twitter_api'] = array(
       '#type' => 'select',
@@ -568,8 +569,6 @@ class Twitter extends MediaTypeBase {
     $display->setComponent(static::MEDIA_ENTITY_TWITTER_DEFAULT_FIELD_NAME, [
       'type' => static::MEDIA_ENTITY_TWITTER_DEFAULT_FIELD_FORMATTER,
     ])->save();
-
-    // @TODO Evaluate if it's necessary to save the 'source_field' config value.
   }
 
 }