diff --git a/core/core.services.yml b/core/core.services.yml
index 18d34b9..f5bc02e 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1281,7 +1281,7 @@ services:
     class: Drupal\Core\Asset\AssetDumper
   library.discovery:
     class: Drupal\Core\Asset\LibraryDiscovery
-    arguments: ['@library.discovery.collector', '@module_handler']
+    arguments: ['@library.discovery.collector', '@module_handler', '@theme.manager']
   library.discovery.collector:
     class: Drupal\Core\Asset\LibraryDiscoveryCollector
     arguments: ['@cache.discovery', '@lock', '@library.discovery.parser']
@@ -1289,7 +1289,7 @@ services:
       - { name: needs_destruction }
   library.discovery.parser:
     class: Drupal\Core\Asset\LibraryDiscoveryParser
-    arguments: ['@app.root', '@module_handler']
+    arguments: ['@app.root', '@module_handler', '@theme.manager']
   library.dependency_resolver:
     class: Drupal\Core\Asset\LibraryDependencyResolver
     arguments: ['@library.discovery']
diff --git a/core/lib/Drupal/Core/Asset/LibraryDiscovery.php b/core/lib/Drupal/Core/Asset/LibraryDiscovery.php
index c79674a..c15eab9 100644
--- a/core/lib/Drupal/Core/Asset/LibraryDiscovery.php
+++ b/core/lib/Drupal/Core/Asset/LibraryDiscovery.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Cache\CacheCollectorInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Theme\ThemeManagerInterface;
 
 /**
  * Discovers available asset libraries in Drupal.
@@ -30,6 +31,13 @@ class LibraryDiscovery implements LibraryDiscoveryInterface {
   protected $moduleHandler;
 
   /**
+   * The theme manager.
+   *
+   * @var \Drupal\Core\Theme\ThemeManagerInterface
+   */
+  protected $themeManager;
+
+  /**
    * The final library definitions, statically cached.
    *
    * hook_library_info_alter() and hook_js_settings_alter() allows modules
@@ -47,9 +55,10 @@ class LibraryDiscovery implements LibraryDiscoveryInterface {
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   The module handler.
    */
-  public function __construct(CacheCollectorInterface $library_discovery_collector, ModuleHandlerInterface $module_handler) {
+  public function __construct(CacheCollectorInterface $library_discovery_collector, ModuleHandlerInterface $module_handler, ThemeManagerInterface $theme_manager) {
     $this->collector = $library_discovery_collector;
     $this->moduleHandler = $module_handler;
+    $this->themeManager = $theme_manager;
   }
 
   /**
@@ -64,6 +73,7 @@ public function getLibrariesByExtension($extension) {
         // specific data for this library; e.g., localization.
         $library_name = "$extension/$name";
         $this->moduleHandler->alter('library', $definition, $library_name);
+        $this->themeManager->alter('library', $definition, $library_name);
         $this->libraryDefinitions[$extension][$name] = $definition;
       }
     }
diff --git a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
index 26ba97a..7e9ba06 100644
--- a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
+++ b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Asset\Exception\InvalidLibraryFileException;
 use Drupal\Core\Asset\Exception\LibraryDefinitionMissingLicenseException;
 use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Theme\ThemeManagerInterface;
 use Drupal\Component\Serialization\Exception\InvalidDataTypeException;
 use Drupal\Component\Serialization\Yaml;
 use Drupal\Component\Utility\NestedArray;
@@ -28,6 +29,13 @@ class LibraryDiscoveryParser {
   protected $moduleHandler;
 
   /**
+   * The theme manager.
+   *
+   * @var \Drupal\Core\Theme\ThemeManagerInterface
+   */
+  protected $themeManager;
+
+  /**
    * The app root.
    *
    * @var string
@@ -42,9 +50,10 @@ class LibraryDiscoveryParser {
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   The module handler.
    */
-  public function __construct($root, ModuleHandlerInterface $module_handler) {
+  public function __construct($root, ModuleHandlerInterface $module_handler, ThemeManagerInterface $theme_manager) {
     $this->root = $root;
     $this->moduleHandler = $module_handler;
+    $this->themeManager = $theme_manager;
   }
 
   /**
@@ -241,6 +250,7 @@ protected function parseLibraryInfo($extension, $path) {
 
     // Allow modules to alter the module's registered libraries.
     $this->moduleHandler->alter('library_info', $libraries, $extension);
+    $this->themeManager->alter('library_info', $libraries, $extension);
 
     return $libraries;
   }