.../src/Plugin/CKEditor5PluginDefinition.php       | 63 +++++-----------------
 .../src/Plugin/CKEditor5PluginManager.php          | 35 +++++++++++-
 .../src/Kernel/CKEditor5PluginManagerTest.php      |  6 +--
 3 files changed, 49 insertions(+), 55 deletions(-)

diff --git a/core/modules/ckeditor5/src/Plugin/CKEditor5PluginDefinition.php b/core/modules/ckeditor5/src/Plugin/CKEditor5PluginDefinition.php
index 3ca1ab5e52..3af202c7c1 100644
--- a/core/modules/ckeditor5/src/Plugin/CKEditor5PluginDefinition.php
+++ b/core/modules/ckeditor5/src/Plugin/CKEditor5PluginDefinition.php
@@ -35,63 +35,22 @@ final class CKEditor5PluginDefinition extends PluginDefinition implements Plugin
    */
   private $drupal;
 
-  /**
-   * Discovered base plugin IDs.
-   *
-   * @var string[]
-   *
-   * @internal
-   */
-  protected static $basePluginIds = [];
-
   /**
    * CKEditor5PluginDefinition constructor.
    *
    * @param array $definition
    *   An array of values from the annotation/YAML.
    *
-   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
+   * @throws \InvalidArgumentException
    */
   public function __construct(array $definition) {
-    $this->id = $id = !isset($definition['base_id'])
-      ? $definition['id']
-      : sprintf("%s:%s", $definition['base_id'], $definition['id']);
-
-    $expected_prefix = sprintf("%s_", $definition['provider']);
-    if (strpos($id, $expected_prefix) !== 0) {
-      throw new InvalidPluginDefinitionException($id, sprintf('The "%s" CKEditor 5 plugin definition must have a plugin ID that starts with "%s".', $id, $expected_prefix));
-    }
-    $this->provider = $definition['provider'];
-
-    try {
-      static::validateCKEditor5Aspects($id, $definition);
-      $this->ckeditor5 = $definition['ckeditor5'];
-
-      $this->validateDrupalAspects($id, $definition);
-      $this->drupal = $definition['drupal'];
-    }
-    catch (InvalidPluginDefinitionException $e) {
-      // If this exception is thrown for a CKEditor 5 plugin definition whose ID
-      // matches a previously seen base plugin ID, it means the deriver did not
-      // generate a valid plugin definition. Re-throw the exception, but tweak
-      // the language for DX: clarify it is for a derived plugin definition.
-      if (!empty(static::$basePluginIds) && preg_match('/^(' . implode('|', static::$basePluginIds) . ').*/', $this->id)) {
-        throw new InvalidPluginDefinitionException($e->getPluginId(), str_replace('plugin definition', 'derived plugin definition', $e->getMessage()));
+    foreach ($definition as $property => $value) {
+      if (property_exists($this, $property)) {
+        $this->{$property} = $value;
       }
-
-      // Allow an invalid plugin definition only if it's yet to be derived.
-      if (isset($definition['drupal']['deriver']) && class_exists($definition['drupal']['deriver'])) {
-        // Pass on all information from the base definition, without validation;
-        // it will be validated later.
-        $this->ckeditor5 = $definition['ckeditor5'] ?? [];
-        $this->drupal = $definition['drupal'];
-        // Track which IDs should be considered base plugin IDs.
-        static::$basePluginIds[] = $this->id;
-        return;
+      else {
+        throw new \InvalidArgumentException(sprintf('Property %s with value %s does not exist on %s.', $property, $value, __CLASS__));
       }
-
-      // Otherwise, the exception was appropriate: re-throw it.
-      throw $e;
     }
   }
 
@@ -118,8 +77,11 @@ public function toArray(): array {
    *   The plugin definition to validate.
    *
    * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
+   *
+   * @internal
+   * @see \Drupal\ckeditor5\Plugin\CKEditor5PluginManager::processDefinition()
    */
-  private static function validateCKEditor5Aspects(string $id, array $definition): void {
+  public static function validateCKEditor5Aspects(string $id, array $definition): void {
     if (!isset($definition['ckeditor5'])) {
       throw new InvalidPluginDefinitionException($id, sprintf('The "%s" CKEditor 5 plugin definition must contain a "ckeditor5" key.', $id));
     }
@@ -159,8 +121,11 @@ private static function validateCKEditor5Aspects(string $id, array $definition):
    *   The plugin definition to validate.
    *
    * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
+   *
+   * @internal
+   * @see \Drupal\ckeditor5\Plugin\CKEditor5PluginManager::processDefinition()
    */
-  private function validateDrupalAspects(string $id, array $definition): void {
+  public function validateDrupalAspects(string $id, array $definition): void {
     if (!isset($definition['drupal'])) {
       throw new InvalidPluginDefinitionException($id, sprintf('The "%s" CKEditor 5 plugin definition must contain a "drupal" key.', $id));
     }
diff --git a/core/modules/ckeditor5/src/Plugin/CKEditor5PluginManager.php b/core/modules/ckeditor5/src/Plugin/CKEditor5PluginManager.php
index b12b2e2d9a..3558ab407b 100644
--- a/core/modules/ckeditor5/src/Plugin/CKEditor5PluginManager.php
+++ b/core/modules/ckeditor5/src/Plugin/CKEditor5PluginManager.php
@@ -73,10 +73,43 @@ protected function getDiscovery() {
    * {@inheritdoc}
    */
   public function processDefinition(&$definition, $plugin_id) {
-    parent::processDefinition($definition, $plugin_id);
     if (!$definition instanceof CKEditor5PluginDefinition) {
       throw new InvalidPluginDefinitionException($plugin_id, sprintf('The "%s" CKEditor 5 plugin definition must extend %s', $plugin_id, CKEditor5PluginDefinition::class));
     }
+
+    // A derived plugin will still have the ID of the derivative, rather than
+    // that of the derived plugin ID (`<base plugin ID>:<derivative ID>`).
+    // Generate an updated CKEditor5PluginDefinition.
+    // @see \Drupal\Component\Plugin\Discovery\DerivativeDiscoveryDecorator::encodePluginId()
+    // @todo Remove this in https://www.drupal.org/project/drupal/issues/2458769.
+    $is_derived = $definition->id() !== $plugin_id;
+    if ($is_derived) {
+      $definition = new CKEditor5PluginDefinition(['id' => $plugin_id] + $definition->toArray());
+    }
+
+    $expected_prefix = sprintf("%s_", $definition->getProvider());
+    $id = $definition->id();
+    if (strpos($id, $expected_prefix) !== 0) {
+      throw new InvalidPluginDefinitionException($id, sprintf('The "%s" CKEditor 5 plugin definition must have a plugin ID that starts with "%s".', $id, $expected_prefix));
+    }
+
+    try {
+      $definition->validateCKEditor5Aspects($id, $definition->toArray());
+      $definition->validateDrupalAspects($id, $definition->toArray());
+    }
+    catch (InvalidPluginDefinitionException $e) {
+      // If this exception is thrown for a derived CKEditor 5 plugin definition,
+      // it means the deriver did not generate a valid plugin definition.
+      // Re-throw the exception, but tweak the language for DX: clarify it is
+      // for a derived plugin definition.
+      if ($is_derived) {
+        throw new InvalidPluginDefinitionException($e->getPluginId(), str_replace('plugin definition', 'derived plugin definition', $e->getMessage()));
+      }
+      // Otherwise, the exception was appropriate: re-throw it.
+      throw $e;
+    }
+
+    parent::processDefinition($definition, $plugin_id);
   }
 
   /**
diff --git a/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php b/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
index 003a6b631b..e92f5eda67 100644
--- a/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
+++ b/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
@@ -1589,7 +1589,6 @@ public function getDerivativeDefinitions($base_plugin_definition) {
     assert($base_plugin_definition instanceof CKEditor5PluginDefinition);
     foreach (['bar', 'baz'] as $derivative) {
       $definition = $base_plugin_definition->toArray();
-      $definition['base_id'] = $base_plugin_definition->id();
       $definition['id'] = $derivative;
       $definition['drupal']['label'] = sprintf("Foo %s", $derivative);
       $this->derivatives[$definition['id']] = new CKEditor5PluginDefinition($definition);
@@ -1634,7 +1633,7 @@ public function getDerivativeDefinitions($base_plugin_definition) {
     elements: false
     deriver: Drupal\ckeditor5_derived_plugin\Plugin\CKEditor5Plugin\SimpleDeriver
 YAML,
-      'The "ckeditor5_derived_plugin_foo:bar" CKEditor 5 derived plugin definition must contain a "ckeditor5.plugins" key.',
+      'The "ckeditor5_derived_plugin_foo:bar" CKEditor 5 derived plugin definition must contain a "ckeditor5" key.',
       $simple_deriver_additional_files,
     ];
 
@@ -1662,7 +1661,6 @@ public function getDerivativeDefinitions($base_plugin_definition) {
     assert($base_plugin_definition instanceof CKEditor5PluginDefinition);
     foreach (['bar', 'baz'] as $derivative) {
       $definition = $base_plugin_definition->toArray();
-      $definition['base_id'] = $base_plugin_definition->id();
       $definition['id'] = $derivative;
       $definition['drupal']['label'] = sprintf("Foo %s", $derivative);
       $this->derivatives[$definition['id']] = $definition;
@@ -1792,7 +1790,6 @@ public function getDerivativeDefinitions($base_plugin_definition) {
     assert($base_plugin_definition instanceof CKEditor5PluginDefinition);
     foreach (['A', 'B'] as $derivative) {
       $definition = $base_plugin_definition->toArray();
-      $definition['base_id'] = $base_plugin_definition->id();
       $definition['id'] = $derivative;
       $definition['drupal']['label'] = sprintf("Foo %s", $derivative);
       $definition['drupal']['elements'] = FALSE;
@@ -1881,7 +1878,6 @@ public function getDerivativeDefinitions($base_plugin_definition) {
     $authentication_providers = array_keys($this->authenticationCollector->getSortedProviders());
     foreach ($authentication_providers as $id) {
       $definition = $base_plugin_definition->toArray();
-      $definition['base_id'] = $base_plugin_definition->id();
       $definition['id'] = $id;
       $definition['drupal']['label'] = sprintf("Foo %s", $id);
       $this->derivatives[$definition['id']] = new CKEditor5PluginDefinition($definition);