diff --git a/core/lib/Drupal/Component/Plugin/Factory/DefaultFactory.php b/core/lib/Drupal/Component/Plugin/Factory/DefaultFactory.php
index d049814..d264c25 100644
--- a/core/lib/Drupal/Component/Plugin/Factory/DefaultFactory.php
+++ b/core/lib/Drupal/Component/Plugin/Factory/DefaultFactory.php
@@ -58,8 +58,11 @@ public function createInstance($plugin_id, array $configuration) {
    *   The appropriate class name.
    */
   public static function getPluginClass($plugin_id, array $plugin_definition = NULL) {
+    if (empty($plugin_definition)) {
+      throw new PluginException(sprintf('The plugin (%s) does not exist.', $plugin_id));
+    }
     if (empty($plugin_definition['class'])) {
-      throw new PluginException(sprintf('The plugin (%s) did not specify an instance class.', $plugin_id));
+      throw new PluginException(sprintf('The plugin (%s) did not specify a class in its definition', $plugin_id));
     }
 
     $class = $plugin_definition['class'];