diff --git a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
index 99abd89..341223a 100644
--- a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
+++ b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
@@ -270,7 +270,7 @@ protected function findDefinitions() {
     // If this plugin was provided by a module that does not exist, remove the
     // plugin definition.
     foreach ($definitions as $plugin_id => $plugin_definition) {
-      if (isset($plugin_definition['provider']) && !in_array($plugin_definition['provider'], array('Core', 'Component')) && !$this->moduleHandler->moduleExists($plugin_definition['provider'])) {
+      if ((is_array($plugin_definition) || ($base_definition = (array) $plugin_definition)) && isset($plugin_definition['provider']) && !in_array($plugin_definition['provider'], array('Core', 'Component')) && !$this->moduleHandler->moduleExists($plugin_definition['provider'])) {
         unset($definitions[$plugin_id]);
       }
     }