diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 552f870..54dd866 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -2089,7 +2089,7 @@ function template_preprocess_table(&$variables) {
   // Flags.
   $is_sticky = !empty($variables['sticky']);
   $is_responsive = !empty($variables['responsive']);
-  $variables['attributes'] = new Attribute(array() + $variables['attributes']);
+  $variables['attributes'] = new Attribute(array('class' => array()) + $variables['attributes']);
 
   // Table headers. (Drupal supports only one, that's why it's called 'header').
   // Headers needed for reference of active sorting