diff --git a/core/lib/Drupal/Core/Utility/LinkGenerator.php b/core/lib/Drupal/Core/Utility/LinkGenerator.php
index 0ec5280..4d26701 100644
--- a/core/lib/Drupal/Core/Utility/LinkGenerator.php
+++ b/core/lib/Drupal/Core/Utility/LinkGenerator.php
@@ -91,6 +91,9 @@ public function generate($text, Url $url) {
       'options' => $url->getOptions(),
     );
 
+    assert('!isset($variables["options"]) || is_array($variables["options"])');
+    assert('!isset($variables["attributes"]) || is_array($variables["attributes"])');
+
     // Merge in default options.
     $variables['options'] += array(
       'attributes' => array(),