diff --git a/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
index 9d6dd1a..31af066 100644
--- a/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -545,10 +545,14 @@ public function renderVar($arg) {
    *   The strings joined together.
    */
   public function safeJoin(\Twig_Environment $env, $value, $glue = '') {
+    if ($value instanceof \Traversable) {
+      $value = iterator_to_array($value, false);
+    }
+
     return implode($glue, array_map(function($item) use ($env) {
       // If $item is not marked safe then it will be escaped.
       return $this->escapeFilter($env, $item, 'html', NULL, TRUE);
-    }, $value));
+    }, (array) $value));
   }
 
 }