diff --git a/core/lib/Drupal/Core/Plugin/Discovery/CacheDecorator.php b/core/lib/Drupal/Core/Plugin/Discovery/CacheDecorator.php
index 40d8b96..a199171 100644
--- a/core/lib/Drupal/Core/Plugin/Discovery/CacheDecorator.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/CacheDecorator.php
@@ -155,7 +155,12 @@ protected function setCachedDefinitions($definitions) {
    * Implements \Drupal\Component\Plugin\Discovery\CachedDiscoveryInterface::clearCachedDefinitions().
    */
   public function clearCachedDefinitions() {
-    if (isset($this->cacheKey)) {
+    // If there are any cache tags, clear cache based on those.
+    if (!empty($this->cacheTags)) {
+      cache($this->cacheBin)->deleteTags($this->cacheTags);
+    }
+    // Otherwise, just delete the specified cache key.
+    else if (isset($this->cacheKey)) {
       cache($this->cacheBin)->delete($this->cacheKey);
     }
     $this->definitions = NULL;
diff --git a/core/modules/system/lib/Drupal/system/Tests/Plugin/CacheDecoratorLanguageTest.php b/core/modules/system/lib/Drupal/system/Tests/Plugin/CacheDecoratorLanguageTest.php
index 56c1d0d..23d01fa 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/CacheDecoratorLanguageTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/CacheDecoratorLanguageTest.php
@@ -7,8 +7,9 @@
 
 namespace Drupal\system\Tests\Plugin;
 
-use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
+use Drupal\plugin_test\Plugin\CachedMockBlockManager;
+use Drupal\simpletest\WebTestBase;
 
 /**
  * Tests that the AlterDecorator fires and respects the alter hook.
@@ -98,8 +99,9 @@ public function testCacheDecoratorLanguage() {
       $this->assertEqual($cache->cid, 'mock_block:' . $langcode, format_string('The !cache cache exists.', array('!cache' => 'mock_block:' . $langcode)));
       $this->assertEqual($cache->expire, 1542646800, format_string('The cache expiration was properly set.'));
     }
-    // Delete cached items tagged with "plugin_test".
-    cache()->deleteTags(array('plugin_test'));
+    // Clear the plugin definitions.
+    $manager = new CachedMockBlockManager();
+    $manager->clearCachedDefinitions();
     foreach ($languages as $langcode) {
       $cache = cache()->get('mock_block:' . $langcode);
       $this->assertFalse($cache, format_string('The !cache cache was properly cleared through the cache::deleteTags() method.', array('!cache' => 'mock_block:' . $langcode)));