diff --git a/core/modules/field/src/Entity/FieldStorageConfig.php b/core/modules/field/src/Entity/FieldStorageConfig.php
index 4e1e2a0..2ed3c24 100644
--- a/core/modules/field/src/Entity/FieldStorageConfig.php
+++ b/core/modules/field/src/Entity/FieldStorageConfig.php
@@ -97,7 +97,7 @@ class FieldStorageConfig extends ConfigEntityBase implements FieldStorageConfigI
    *
    * @var array
    */
-  public $settings = array();
+  protected $settings = array();
 
   /**
    * The field cardinality.
diff --git a/core/modules/field/src/Tests/FieldStorageCrudTest.php b/core/modules/field/src/Tests/FieldStorageCrudTest.php
index 2e7e840..e4a2b1a 100644
--- a/core/modules/field/src/Tests/FieldStorageCrudTest.php
+++ b/core/modules/field/src/Tests/FieldStorageCrudTest.php
@@ -431,7 +431,7 @@ function testUpdateForbid() {
         'unchangeable' => 0
     )));
     $field_storage->save();
-    $field_storage->settings['changeable']++;
+    $field_storage->setSetting('changeable', $field_storage->getSetting('changeable') + 1);
     try {
       $field_storage->save();
       $this->pass(t("A changeable setting can be updated."));
@@ -439,7 +439,7 @@ function testUpdateForbid() {
     catch (FieldStorageDefinitionUpdateForbiddenException $e) {
       $this->fail(t("An unchangeable setting cannot be updated."));
     }
-    $field_storage->settings['unchangeable']++;
+    $field_storage->setSetting('unchangeable', $field_storage->getSetting('unchangeable') + 1);
     try {
       $field_storage->save();
       $this->fail(t("An unchangeable setting can be updated."));