diff --git a/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
index 0128c66..52d91fd 100644
--- a/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -159,6 +159,7 @@ protected function setOverriddenData() {
     }
     if (isset($this->settingsOverrides) && is_array($this->settingsOverrides)) {
       $this->overriddenData = NestedArray::mergeDeepArray(array($this->overriddenData, $this->settingsOverrides), TRUE);
+      $this->overriddenData['isImmutable'] = TRUE;
     }
     return $this;
   }
@@ -285,6 +286,7 @@ public function getOriginal($key = '', $apply_overrides = TRUE) {
       }
       if (isset($this->settingsOverrides) && is_array($this->settingsOverrides)) {
         $original_data = NestedArray::mergeDeepArray(array($original_data, $this->settingsOverrides), TRUE);
+        $original_data['isImmutable'] = TRUE;
       }
     }
 
diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
index 08e7e19..5d72ada 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
@@ -4,6 +4,7 @@
 
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Cache\Cache;
+use Drupal\Core\Config\ImmutableConfigException;
 use Drupal\Core\Config\Schema\SchemaIncompleteException;
 use Drupal\Core\Entity\Entity;
 use Drupal\Core\Config\ConfigDuplicateUUIDException;
@@ -107,6 +108,13 @@
   protected $trustedData = FALSE;
 
   /**
+   * The entity may contain overridden values and may therefore not be saved.
+   *
+   * @var bool
+   */
+  protected $isImmutable = FALSE;
+
+  /**
    * {@inheritdoc}
    */
   public function __construct(array $values, $entity_type) {
@@ -630,10 +638,18 @@ public function hasTrustedData() {
     return $this->trustedData;
   }
 
+  public function isImmutable() {
+    return $this->isImmutable;
+  }
+
   /**
    * {@inheritdoc}
    */
   public function save() {
+    if ($this->isImmutable()) {
+      throw new ImmutableConfigException("Can not save immutable configuration entity {$this->id()}. Load the entity via \\Drupal\\Core\\Config\\Entity\\ConfigEntityStorageInterface::loadOverrideFree() / ::loadMultipleOverrideFree() to retrieve a mutable configuration entity object");
+    }
+
     $return = parent::save();
     $this->trustedData = FALSE;
     return $return;
diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php
index 248701e..6f68d7f 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php
@@ -217,4 +217,13 @@ public function trustData();
    */
   public function hasTrustedData();
 
+  /**
+   * Returns whether the entity might contain overridden values and may
+   * therefore not be saved.
+   * 
+   * @return bool
+   *   TRUE if the entity is immutable, FALSE otherwise.
+   */
+  public function isImmutable();
+
 }
diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
index 3834dae..35e8b30 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
@@ -5,6 +5,7 @@
 use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Config\ConfigImporterException;
+use Drupal\Core\Config\ImmutableConfigException;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityMalformedException;
 use Drupal\Core\Entity\EntityStorageBase;
@@ -256,6 +257,11 @@ public function save(EntityInterface $entity) {
       throw new ConfigEntityIdLengthException("Configuration entity ID {$entity->get($this->idKey)} exceeds maximum allowed length of " . self::MAX_ID_LENGTH . " characters.");
     }
 
+    // Ensure an immutable configuration entity is not saved.
+    if ($entity->isImmutable()) {
+      throw new ImmutableConfigException("Can not save immutable configuration entity {$entity->id()}. Load the entity via \\Drupal\\Core\\Config\\Entity\\ConfigEntityStorageInterface::loadOverrideFree() / ::loadMultipleOverrideFree() to retrieve a mutable configuration entity object");
+    }
+
     return parent::save($entity);
   }
 
diff --git a/core/modules/views_ui/src/ViewUI.php b/core/modules/views_ui/src/ViewUI.php
index 6195c8c..9db425e 100644
--- a/core/modules/views_ui/src/ViewUI.php
+++ b/core/modules/views_ui/src/ViewUI.php
@@ -1348,4 +1348,11 @@ public function addCacheTags(array $cache_tags) {
     return $this->storage->addCacheTags($cache_tags);
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function isImmutable() {
+    return $this->storage->isImmutable();
+  }
+
 }
diff --git a/core/tests/Drupal/KernelTests/Core/Config/ConfigEntityOverrideTest.php b/core/tests/Drupal/KernelTests/Core/Config/ConfigEntityOverrideTest.php
index 8d62875..4a5e2dd 100644
--- a/core/tests/Drupal/KernelTests/Core/Config/ConfigEntityOverrideTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Config/ConfigEntityOverrideTest.php
@@ -86,8 +86,7 @@ function testConfEntityOverride() {
     try {
       /** @var \Drupal\config_test\Entity\ConfigTest $config_entity */
       $config_entity = $config_test_storage->load('dotted.default');
-      $expected_original_data['weight'] = 420;
-      $config_entity->weight = $expected_original_data['weight'];
+      $config_entity->weight = 240;
       $config_entity->save();
     } catch (\Exception $e) {}