diff --git a/core/lib/Drupal/Core/Mail/MailManager.php b/core/lib/Drupal/Core/Mail/MailManager.php
index 13a1c7d..102a012 100644
--- a/core/lib/Drupal/Core/Mail/MailManager.php
+++ b/core/lib/Drupal/Core/Mail/MailManager.php
@@ -154,16 +154,7 @@ public function getInstance(array $options) {
     }
 
     if (empty($this->instances[$plugin_id])) {
-      $plugin = $this->createInstance($plugin_id);
-      if (is_subclass_of($plugin, '\Drupal\Core\Mail\MailInterface')) {
-        $this->instances[$plugin_id] = $plugin;
-      }
-      else {
-        throw new InvalidPluginDefinitionException($plugin_id, String::format('Class %class does not implement interface %interface', array(
-          '%class' => get_class($plugin),
-          '%interface' => 'Drupal\Core\Mail\MailInterface',
-        )));
-      }
+      $this->instances[$plugin_id] = $this->createInstance($plugin_id);
     }
     return $this->instances[$plugin_id];
   }