diff --git a/core/lib/Drupal/Core/Field/PluginSettingsBase.php b/core/lib/Drupal/Core/Field/PluginSettingsBase.php
index fb8e07b..480df01 100644
--- a/core/lib/Drupal/Core/Field/PluginSettingsBase.php
+++ b/core/lib/Drupal/Core/Field/PluginSettingsBase.php
@@ -24,6 +24,13 @@
   protected $settings = array();
 
   /**
+   * Settings from other modules.
+   *
+   * @var array
+   */
+  protected $third_party_settings = array();
+
+  /**
    * Whether default settings have been merged into the current $settings.
    *
    * @var bool
@@ -84,4 +91,40 @@ public function setSetting($key, $value) {
     return $this;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getThirdPartySettings() {
+    if (isset($this->settings['third_party'])) {
+      return $this->settings['third_party'];
+    }
+    return array();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getThirdPartySetting($module, $key) {
+    if (isset($this->settings['third_party'][$module][$key])) {
+      return $this->settings['third_party'][$module][$key];
+    }
+    return NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setThirdPartySetting($module, $key, $value) {
+    $this->settings['third_party'][$module][$key] = $value;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setThirdPartySettings($module, array $settings) {
+    $this->settings['third_party'][$module] = $settings;
+    return $this;
+  }
+
 }
diff --git a/core/lib/Drupal/Core/Field/PluginSettingsInterface.php b/core/lib/Drupal/Core/Field/PluginSettingsInterface.php
index 41dd942..cf696b9 100644
--- a/core/lib/Drupal/Core/Field/PluginSettingsInterface.php
+++ b/core/lib/Drupal/Core/Field/PluginSettingsInterface.php
@@ -70,7 +70,7 @@ public function setSetting($key, $value);
    * The array is keyed by the third-party module which provides the settings,
    * and includes defaults for missing settings.
    *
-   * @return mixed
+   * @return array
    *   The array of settings.
    */
   public function getThirdPartySettings();
@@ -83,8 +83,8 @@ public function getThirdPartySettings();
    * @param string $key
    *   The setting name.
    *
-   * @return mixed
-   *   The setting value.
+   * @return mixed|NULL
+   *   The setting value. Returns NULL if the setting does not exist.
    */
   public function getThirdPartySetting($module, $key);
 
diff --git a/core/modules/field/tests/modules/field_test/field_test.module b/core/modules/field/tests/modules/field_test/field_test.module
index 8245815..3163dec 100644
--- a/core/modules/field/tests/modules/field_test/field_test.module
+++ b/core/modules/field/tests/modules/field_test/field_test.module
@@ -159,11 +159,10 @@ function field_test_query_efq_metadata_test_alter(&$query) {
  * Implements hook_field_widget_third_party_settings_form().
  */
 function field_test_field_widget_third_party_settings_form($plugin, \Drupal\Core\Field\FieldDefinitionInterface $field_definition, $form_mode, $form, $form_state) {
-  $third_party_settings = $plugin->getSetting('third_party_settings');
   $element['field_test_widget_third_party_settings_form'] = array(
     '#type' => 'textfield',
     '#title' => t('3rd party widget settings form'),
-    '#default_value' => $third_party_settings['field_test'],
+    '#default_value' => $plugin->getThirdPartySetting('field_test', 'field_test_widget_test'),
   );
   return $element;
 }
@@ -180,11 +179,10 @@ function field_test_field_widget_settings_summary_alter(&$summary, $context) {
  * Implements hook_field_formatter_third_party_settings_form().
  */
 function field_test_field_formatter_third_party_settings_form($plugin, \Drupal\Core\Field\FieldDefinitionInterface $field_definition, $view_mode, $form, $form_state) {
-  $third_party_settings = $plugin->getSetting('third_party_settings');
   $element['field_test_field_formatter_third_party_settings_form'] = array(
     '#type' => 'textfield',
     '#title' => t('3rd party formatter settings form'),
-    '#default_value' => $third_party_settings['field_test'],
+    '#default_value' => $plugin->getThirdPartySetting('field_test', 'field_test_formatter_test'),
   );
   return $element;
 }
diff --git a/core/modules/field_ui/field_ui.api.php b/core/modules/field_ui/field_ui.api.php
index b2b8d4e..6e6687a 100644
--- a/core/modules/field_ui/field_ui.api.php
+++ b/core/modules/field_ui/field_ui.api.php
@@ -34,11 +34,10 @@ function hook_field_formatter_third_party_settings_form($plugin, \Drupal\Core\Fi
   // Add a 'my_setting' checkbox to the settings form for 'foo_formatter' field
   // formatters.
   if ($plugin->getPluginId() == 'foo_formatter') {
-    $third_party_settings = $plugin->getSetting('third_party_settings');
     $element['my_setting'] = array(
       '#type' => 'checkbox',
       '#title' => t('My setting'),
-      '#default_value' => $third_party_settings['my_setting'],
+      '#default_value' => $plugin->getThirdPartySetting('my_module', 'my_setting'),
     );
   }
   return $element;
@@ -68,11 +67,10 @@ function hook_field_widget_third_party_settings_form($plugin, \Drupal\Core\Field
   // Add a 'my_setting' checkbox to the settings form for 'foo_widget' field
   // widgets.
   if ($plugin->getPluginId() == 'foo_widget') {
-    $third_party_settings = $plugin->getSetting('third_party_settings');
     $element['my_setting'] = array(
       '#type' => 'checkbox',
       '#title' => t('My setting'),
-      '#default_value' => $third_party_settings['my_setting'],
+      '#default_value' => $plugin->getThirdPartySetting('my_module', 'my_setting'),
     );
   }
   return $element;
@@ -95,8 +93,7 @@ function hook_field_formatter_settings_summary_alter(&$summary, $context) {
   // Append a message to the summary when an instance of foo_formatter has
   // mysetting set to TRUE for the current view mode.
   if ($context['formatter']->getPluginId() == 'foo_formatter') {
-    $third_party_settings = $plugin->getSetting('third_party_settings');
-    if (isset($third_party_settings['my_setting']) && $third_party_settings['my_setting']) {
+    if ($context['formatter']->getThirdPartySetting('my_module', 'my_setting')) {
       $summary[] = t('My setting enabled.');
     }
   }
@@ -119,8 +116,7 @@ function hook_field_widget_settings_summary_alter(&$summary, $context) {
   // Append a message to the summary when an instance of foo_widget has
   // mysetting set to TRUE for the current view mode.
   if ($context['widget']->getPluginId() == 'foo_widget') {
-    $third_party_settings = $plugin->getSetting('third_party_settings');
-    if (isset($third_party_settings['my_setting']) && $third_party_settings['my_setting']) {
+    if ($context['widget']->getThirdPartySetting('my_module', 'my_setting')) {
       $summary[] = t('My setting enabled.');
     }
   }
diff --git a/core/modules/field_ui/src/Tests/ManageDisplayTest.php b/core/modules/field_ui/src/Tests/ManageDisplayTest.php
index 11c10fe..cc3a851 100644
--- a/core/modules/field_ui/src/Tests/ManageDisplayTest.php
+++ b/core/modules/field_ui/src/Tests/ManageDisplayTest.php
@@ -101,7 +101,7 @@ function testFormatterUI() {
 
     // Assert that the field added in
     // field_test_field_formatter_third_party_settings_form() is present.
-    $fieldname = 'fields[field_test][settings_edit_form][third_party][field_test][field_test_field_formatter_third_party_settings_form]';
+    $fieldname = 'fields[field_test][settings_edit_form][settings][third_party][field_test][field_test_field_formatter_third_party_settings_form]';
     $this->assertField($fieldname, 'The field added in hook_field_formatter_third_party_settings_form() is present on the settings form.');
     $edit = array($fieldname => 'foo');
     $this->drupalPostAjaxForm(NULL, $edit, "field_test_plugin_settings_update");
@@ -194,7 +194,7 @@ public function testWidgetUI() {
 
     // Assert that the field added in
     // field_test_field_widget_third_party_settings_form() is present.
-    $fieldname = 'fields[field_test][settings_edit_form][third_party][field_test][field_test_field_widget_third_party_settings_form]';
+    $fieldname = 'fields[field_test][settings_edit_form][settings][third_party][field_test][field_test_widget_third_party_settings_form]';
     $this->assertField($fieldname, 'The field added in hook_field_widget_third_party_settings_form() is present on the settings form.');
     $edit = array($fieldname => 'foo');
     $this->drupalPostAjaxForm(NULL, $edit, "field_test_plugin_settings_update");