diff --git a/src/MediaBundleForm.php b/src/MediaBundleForm.php
index e8d0b37..014a538 100644
--- a/src/MediaBundleForm.php
+++ b/src/MediaBundleForm.php
@@ -316,7 +316,6 @@ class MediaBundleForm extends EntityForm {
     $plugin_configuration = !empty($this->configurableInstances[$plugin]['plugin_config']) ? $this->configurableInstances[$plugin]['plugin_config'] : [];
     $instance = $this->mediaTypeManager->createInstance($plugin, $plugin_configuration);
     $instance->submitConfigurationForm($form, $form_state);
-
   }
 
   /**
diff --git a/src/MediaTypeDefaultFieldTrait.php b/src/MediaTypeDefaultFieldTrait.php
index 83d40be..70053ff 100644
--- a/src/MediaTypeDefaultFieldTrait.php
+++ b/src/MediaTypeDefaultFieldTrait.php
@@ -11,13 +11,17 @@ use Drupal\field\Entity\FieldStorageConfig;
 
 /**
  * To exhibit by derivatives of Drupal\media_entity\MediaTypeBase.
- * 
- * Implements most of the behaviour required for a single source field that may
+ *
+ * Implements most of the behavior required for a single source field that may
  * be populated with a default field upon creation of a bundle.
+ *
+ * You will need to add a source_field key to your configuration schema.
  */
 trait MediaTypeDefaultFieldTrait {
   use StringTranslationTrait;
 
+  protected $defaultSourceFieldName;
+
   /**
    * Produce an array of allowed field types for the source field.
    *
@@ -28,11 +32,6 @@ trait MediaTypeDefaultFieldTrait {
   abstract public function allowedSourceFieldTypes();
 
   /**
-   * Return the default source field's name.
-   */
-  abstract public function defaultSourceFieldName();
-
-  /**
    * Return the default source field's type.
    */
   abstract public function defaultSourceFieldType();
@@ -54,12 +53,12 @@ trait MediaTypeDefaultFieldTrait {
 
   /**
    * Produce a form fragment to configure the source field.
-   * 
+   *
    * To be called from a media type's buildConfigurationForm() method.
-   * 
+   *
    * @param array $form
    *   The $form array as passed to the buildConfigurationForm().
-   * 
+   *
    * @param \Drupal\Core\Form\FormStateInterface $form_state
    * @return array
    */
@@ -76,24 +75,28 @@ trait MediaTypeDefaultFieldTrait {
       }
     }
 
-    // Select the source field. Only show when the bundle is not new, so there
-    // will potentially be fields to select.
+    // Add a checkbox to allow the field being created automatically on save.
+    // Only include it when the bundle is new, so we can use its presence to
+    // know we can safely override the source field configuration.
+    if ($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,
+      ];
+    }
+
+    // Select the source field. Only show it when the bundle is not new, so
+    // there will potentially be fields to select.
     $form['source_field'] = array(
       '#type' => 'select',
       '#title' => $this->t('Field with source information'),
-      '#default_value' => empty($this->configuration['source_field']) ? $this->defaultSourceFieldName() : $this->configuration['source_field'],
+      '#default_value' => $this->configuration['source_field'],
       '#options' => $options,
       '#access' => !$bundle->isNew(),
     );
 
-    // Add a checkbox to allow the field being created automatically on save.
-    $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(),
-    ];
 
     return $form;
   }
@@ -102,7 +105,7 @@ trait MediaTypeDefaultFieldTrait {
    * {@inheritdoc}
    */
   public function reactOnBundleCreated($bundle_name, $entity_type_id) {
-    if (!empty($this->configuration['create_source_field'])) {
+    if (isset($this->defaultSourceFieldName)) {
       $this->createDefaultSourceField($bundle_name);
     }
   }
@@ -112,22 +115,23 @@ trait MediaTypeDefaultFieldTrait {
    */
   public function createDefaultSourceField($bundle_name) {
 
-    // @todo Sanity-check: defaultSourceFieldType is actually allowed.
-
-    // Create / load the field storage.
-    if (!$storage = FieldStorageConfig::loadByName('media', $this->defaultSourceFieldName())) {
-      $storage = FieldStorageConfig::create([
-        'field_name' => $this->defaultSourceFieldName(),
-        'entity_type' => 'media',
-        'type' => $this->defaultSourceFieldType(),
-      ]);
-      $storage->save();
+    if (!in_array($this->defaultSourceFieldType(), $this->allowedSourceFieldTypes())) {
+      throw new \LogicException('Default source field type is not within the allowed field types.');
     }
 
+    $field_name = $this->defaultSourceFieldName;
+
+    $storage = FieldStorageConfig::create([
+      'field_name' => $field_name,
+      'entity_type' => 'media',
+      'type' => $this->defaultSourceFieldType(),
+    ]);
+    $storage->save();
+
     // Create the field instance.
     FieldConfig::create([
       'entity_type' => 'media',
-      'field_name' => $this->defaultSourceFieldName(),
+      'field_name' => $field_name,
       'label' => $this->defaultSourceFieldLabel(),
       'required' => TRUE,
       'bundle' => $bundle_name,
@@ -141,7 +145,7 @@ trait MediaTypeDefaultFieldTrait {
       'mode' => 'default',
       'status' => TRUE,
     ]);
-    $form_display->setComponent($this->defaultSourceFieldName(), [
+    $form_display->setComponent($field_name, [
       'type' => $this->defaultSourceFieldWidget(),
     ])->save();
 
@@ -153,9 +157,54 @@ trait MediaTypeDefaultFieldTrait {
       'mode' => 'default',
       'status' => TRUE,
     ]);
-    $display->setComponent($this->defaultSourceFieldName(), [
+    $display->setComponent($field_name, [
       'type' => $this->defaultSourceFieldFormatter(),
     ])->save();
   }
 
+  /**
+   * Determine a free field name to use as the default field.
+   *
+   * @return string
+   *   An appropriate field name that was determined to be available.
+   */
+  protected function determineDefaultSourceFieldName() {
+    // Determine a unique field name.
+    if (isset($this->defaultSourceFieldName)) {
+      return $this->defaultSourceFieldName;
+    }
+
+    $base_field_name = 'field_media_' . $this->getPluginId();
+    $field_name_candidate = $base_field_name;
+    $postfix = '';
+    while (FieldStorageConfig::loadByName('media', $field_name_candidate)) {
+      if (empty($postfix)) {
+        $postfix = 1;
+      }
+      else {
+        $postfix++;
+      }
+
+      $field_name_candidate = $base_field_name . '_' . $postfix;
+    }
+
+    return $this->defaultSourceFieldName = $field_name_candidate;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setConfiguration(array $configuration) {
+    // Take out the create_source_field key when present so it doesn't end up
+    // in the configuration. Record it was set so we can later decide to
+    // actually create the field. Determine the field name here so it correctly
+    // is entered into the configuration.
+    if (isset($configuration['create_source_field'])) {
+      unset($configuration['create_source_field']);
+      $configuration['source_field'] = $this->determineDefaultSourceFieldName();
+    }
+
+    parent::setConfiguration($configuration);
+  }
+
 }
diff --git a/src/MediaTypeInterface.php b/src/MediaTypeInterface.php
index 4cda123..632dcec 100644
--- a/src/MediaTypeInterface.php
+++ b/src/MediaTypeInterface.php
@@ -95,15 +95,4 @@ interface MediaTypeInterface extends PluginInspectionInterface, ConfigurablePlug
    */
   public function reactOnBundleCreated($bundle_name, $entity_type_id);
 
-  /**
-   * Create a default source field.
-   *
-   * Plugins defining media bundles are strongly encouraged to provide a default
-   * source field to all fields used as source, when a new bundle is created.
-   *
-   * @param string $bundle_name
-   *   The machine-name of the bundle recently created.
-   */
-  public function createDefaultSourceField($bundle_name);
-
 }
diff --git a/tests/modules/media_entity_test_type/src/Plugin/MediaEntity/Type/TestType.php b/tests/modules/media_entity_test_type/src/Plugin/MediaEntity/Type/TestType.php
index 18571f1..5ba6800 100644
--- a/tests/modules/media_entity_test_type/src/Plugin/MediaEntity/Type/TestType.php
+++ b/tests/modules/media_entity_test_type/src/Plugin/MediaEntity/Type/TestType.php
@@ -7,6 +7,7 @@ use Drupal\Core\Entity\Entity\EntityViewDisplay;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\media_entity\MediaTypeDefaultFieldTrait;
 use Drupal\media_entity\Plugin\MediaEntity\Type\Generic;
 
 /**
@@ -19,21 +20,42 @@ use Drupal\media_entity\Plugin\MediaEntity\Type\Generic;
  * )
  */
 class TestType extends Generic {
+  use MediaTypeDefaultFieldTrait;
 
   /**
-   * The name of the default source field on the media entity.
+   * {@inheritdoc}
+   */
+  public function allowedSourceFieldTypes() {
+    return ['string'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultSourceFieldLabel() {
+    return $this->t('Test source');
+  }
+
+  /**
+   * {@inheritdoc}
    */
-  const MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_NAME = 'field_media_test_type';
+  public function defaultSourceFieldType() {
+    return 'string';
+  }
 
   /**
-   * The id of the widget to be used when creating the default source field.
+   * {@inheritdoc}
    */
-  const MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_WIDGET = 'string_textfield';
+  public function defaultSourceFieldWidget() {
+    return 'string_textfield';
+  }
 
   /**
-   * The id of the formatter to be used when creating the default source field.
+   * {@inheritdoc}
    */
-  const MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_FORMATTER = 'string';
+  public function defaultSourceFieldFormatter() {
+    return 'string';
+  }
 
   /**
    * {@inheritdoc}
@@ -65,96 +87,11 @@ class TestType extends Generic {
       '#default_value' => empty($this->configuration['test_config_value']) ? NULL : $this->configuration['test_config_value'],
     ];
 
-    $options = [];
-    $allowed_field_types = ['string'];
-    /** @var \Drupal\media_entity\MediaBundleInterface $bundle */
-    $bundle = $form_state->getFormObject()->getEntity();
-    foreach ($this->entityFieldManager->getFieldDefinitions('media', $bundle->id()) as $field_name => $field) {
-      if (in_array($field->getType(), $allowed_field_types) && !$field->getFieldStorageDefinition()->isBaseField()) {
-        $options[$field_name] = $field->getLabel();
-      }
-    }
+    $form = $this->defaultFieldConfigurationForm($form, $form_state);
 
-    $form['source_field'] = array(
-      '#type' => 'select',
-      '#title' => $this->t('Field with source information'),
-      '#description' => $this->t('Field on media entity that stores the source information. You can create a bundle without selecting a value for this dropdown initially. This dropdown can be populated after adding fields to the bundle.'),
-      '#default_value' => empty($this->configuration['source_field']) ? self::MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_NAME : $this->configuration['source_field'],
-      '#options' => $options,
-    );
-
-    // Add a checkbox to allow the field being created automatically on save.
-    if (empty($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['source_field']['#description'] = $this->t('Field on media entity that stores the source information.');
 
     return $form;
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function reactOnBundleCreated($bundle_name, $entity_type_id) {
-    if (!empty($this->configuration['create_source_field'])) {
-      $this->createDefaultSourceField($bundle_name);
-    }
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function createDefaultSourceField($bundle_name) {
-
-    // Create / load the field storage.
-    if (!$storage = FieldStorageConfig ::loadByName('media', static::MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_NAME)) {
-      $storage = FieldStorageConfig::create([
-        'field_name' => static::MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_NAME,
-        'entity_type' => 'media',
-        'type' => 'string',
-      ]);
-      $storage->save();
-    }
-
-    // Create the field instance.
-    FieldConfig::create([
-      'entity_type' => 'media',
-      'field_name' => static::MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_NAME,
-      'label' => $this->t('Tweet URL'),
-      'required' => TRUE,
-      'bundle' => $bundle_name,
-    ])->save();
-
-    // Make the field visible on the form display.
-    /** @var \Drupal\Core\Entity\Display\EntityFormDisplayInterface $form_display */
-    $form_display = EntityFormDisplay::create([
-      'targetEntityType' => 'media',
-      'bundle' => $bundle_name,
-      'mode' => 'default',
-      'status' => TRUE,
-    ]);
-    $form_display->setComponent(static::MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_NAME, [
-      'type' => static::MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_WIDGET,
-    ])->save();
-
-    // Make the field visible on the media entity itself.
-    /** @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface $display */
-    $display = EntityViewDisplay::create([
-      'targetEntityType' => 'media',
-      'bundle' => $bundle_name,
-      'mode' => 'default',
-      'status' => TRUE,
-    ]);
-    $display->setComponent(static::MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_NAME, [
-      'type' => static::MEDIA_ENTITY_TEST_TYPE_DEFAULT_FIELD_FORMATTER,
-    ])->save();
-
-    // @TODO Evaluate if it's necessary to save the 'source_field' config value.
-  }
-
 }