diff --git a/core/modules/responsive_image/responsive_image.module b/core/modules/responsive_image/responsive_image.module
index 925fe3c..5ea2408 100644
--- a/core/modules/responsive_image/responsive_image.module
+++ b/core/modules/responsive_image/responsive_image.module
@@ -115,7 +115,10 @@ function template_preprocess_responsive_image_formatter(&$variables) {
     $attributes['title'] = $item->title;
   }
   $attributes['alt'] = $item->alt;
-  $attributes += $variables['item_attributes'];
+  // Concate only if array.
+  if (is_array($variables['item_attributes'])) {
+    $attributes += $variables['item_attributes'];
+  }
   if (($entity = $item->entity) && empty($item->uri)) {
     $variables['responsive_image']['#uri'] = $entity->getFileUri();
   }