diff --git a/core/lib/Drupal/Core/Config/Entity/ThirdPartySettingsTrait.php b/core/lib/Drupal/Core/Config/Entity/ThirdPartySettingsTrait.php
index b37367f..1942c9b 100644
--- a/core/lib/Drupal/Core/Config/Entity/ThirdPartySettingsTrait.php
+++ b/core/lib/Drupal/Core/Config/Entity/ThirdPartySettingsTrait.php
@@ -10,15 +10,23 @@
 /**
  * Provides generic implementation of ThirdPartySettingsInterface.
  *
- * The default property used to store third party settings is 'settings'. To
- * override for a specific implement set $thirdPartySettingKey in the
- * constructor.
+ * The name of the property used to store third party settings is
+ * 'third_party_settings'. You need to provide configuration schema for that
+ * setting to ensure it is persisted. See 'third_party_settings' defined on
+ * field_config_base and other 'field_config.third_party.*' types.
  *
  * @see \Drupal\Core\Config\Entity\ThirdPartySettingsInterface
  */
 trait ThirdPartySettingsTrait {
 
-  protected $thirdPartySettingKey = 'third_party_settings';
+  /**
+   * Third party entity settings.
+   *
+   * An array of key/value pairs keyed by provider.
+   *
+   * @var array
+   */
+  protected $third_party_settings = array();
 
   /**
    * Sets the value of a third-party setting.
@@ -33,7 +41,7 @@
    * @return $this
    */
   public function setThirdPartySetting($module, $key, $value) {
-    $this->{$this->thirdPartySettingKey}[$module][$key] = $value;
+    $this->third_party_settings[$module][$key] = $value;
     return $this;
   }
 
@@ -51,8 +59,8 @@ public function setThirdPartySetting($module, $key, $value) {
    *   The value.
    */
   public function getThirdPartySetting($module, $key, $default = NULL) {
-    if (isset($this->{$this->thirdPartySettingKey}[$module][$key])) {
-      return $this->{$this->thirdPartySettingKey}[$module][$key];
+    if (isset($this->third_party_settings[$module][$key])) {
+      return $this->third_party_settings[$module][$key];
     }
     else {
       return $default;
@@ -71,11 +79,11 @@ public function getThirdPartySetting($module, $key, $default = NULL) {
    *   The value.
    */
   public function unsetThirdPartySetting($module, $key) {
-    unset($this->{$this->thirdPartySettingKey}[$module][$key]);
+    unset($this->third_party_settings[$module][$key]);
     // If the third party is no longer storing any information completely remove
     // the setting.
-    if (empty($this->{$this->thirdPartySettingKey}[$module])) {
-      unset($this->{$this->thirdPartySettingKey}[$module]);
+    if (empty($this->third_party_settings[$module])) {
+      unset($this->third_party_settings[$module]);
     }
     return $this;
   }
@@ -87,7 +95,7 @@ public function unsetThirdPartySetting($module, $key) {
    *   The list of third parties.
    */
   public function getThirdPartyProviders() {
-    return array_keys($this->{$this->thirdPartySettingKey});
+    return array_keys($this->third_party_settings);
   }
 
 }
diff --git a/core/lib/Drupal/Core/Field/FieldConfigBase.php b/core/lib/Drupal/Core/Field/FieldConfigBase.php
index 189b417..462f98b 100644
--- a/core/lib/Drupal/Core/Field/FieldConfigBase.php
+++ b/core/lib/Drupal/Core/Field/FieldConfigBase.php
@@ -99,15 +99,6 @@
   public $settings = array();
 
   /**
-   * Third party field-type specific settings.
-   *
-   * An arrays of key/value pairs keyed by provider.
-   *
-   * @var array
-   */
-  protected $third_party_settings = array();
-
-  /**
    * Flag indicating whether the field is required.
    *
    * TRUE if a value for this field is required when used with this bundle,
diff --git a/core/tests/Drupal/Tests/Core/Config/Entity/Fixtures/ConfigEntityBaseWithThirdPartySettings.php b/core/tests/Drupal/Tests/Core/Config/Entity/Fixtures/ConfigEntityBaseWithThirdPartySettings.php
index 9d5db7c..6834e63 100644
--- a/core/tests/Drupal/Tests/Core/Config/Entity/Fixtures/ConfigEntityBaseWithThirdPartySettings.php
+++ b/core/tests/Drupal/Tests/Core/Config/Entity/Fixtures/ConfigEntityBaseWithThirdPartySettings.php
@@ -20,5 +20,4 @@
 abstract class ConfigEntityBaseWithThirdPartySettings extends ConfigEntityBase implements ThirdPartySettingsInterface {
   use ThirdPartySettingsTrait;
 
-  protected $third_party_settings = array();
 }
diff --git a/core/tests/Drupal/Tests/Core/Config/Entity/ThirdPartySettingsTraitTest.php b/core/tests/Drupal/Tests/Core/Config/Entity/ThirdPartySettingsTraitTest.php
index 3304c48..ce43331 100644
--- a/core/tests/Drupal/Tests/Core/Config/Entity/ThirdPartySettingsTraitTest.php
+++ b/core/tests/Drupal/Tests/Core/Config/Entity/ThirdPartySettingsTraitTest.php
@@ -21,15 +21,13 @@ class ThirdPartySettingsTraitTest extends UnitTestCase {
    * @covers ::setThirdPartySetting
    * @covers ::unsetThirdPartySetting
    * @covers ::getThirdPartyProviders
-   *
-   * @dataProvider providerTestThirdPartySettings
    */
-  public function testThirdPartySettings($third_party_settings_key = NULL) {
+  public function testThirdPartySettings() {
     $key = 'test';
     $third_party = 'test_provider';
     $value = $this->getRandomGenerator()->string();
 
-    $trait_object = new TestThirdPartySettingsTrait($third_party_settings_key);
+    $trait_object = new TestThirdPartySettingsTrait();
 
     // Test getThirdPartySetting() with no settings.
     $this->assertEquals($value, $trait_object->getThirdPartySetting($third_party, $key, $value));
@@ -48,20 +46,8 @@ public function testThirdPartySettings($third_party_settings_key = NULL) {
     $trait_object->unsetThirdPartySetting('test_provider2', $key);
     $this->assertEquals(array($third_party), $trait_object->getThirdPartyProviders());
   }
-
-  public function providerTestThirdPartySettings() {
-    return array(array(NULL), array('settings'));
-  }
 }
 
 class TestThirdPartySettingsTrait {
   use ThirdPartySettingsTrait;
-
-  public function __construct($third_party_settings_key = NULL) {
-    if ($third_party_settings_key) {
-      $this->thirdPartySettingKey = $third_party_settings_key;
-    }
-    $this->{$this->thirdPartySettingKey} = array();
-  }
-
 }