diff --git a/core/modules/views/views.theme.inc b/core/modules/views/views.theme.inc
index e3b4b37..8000176 100644
--- a/core/modules/views/views.theme.inc
+++ b/core/modules/views/views.theme.inc
@@ -575,7 +575,9 @@ function template_preprocess_views_view_table(&$vars) {
       }
 
       // Improves accessibility of complex tables.
-      $vars['field_classes'][$field][$num]['headers'][] = (isset($vars['header_classes'][$field]['id'])) ? $vars['header_classes'][$field]['id'] : '';
+      if (isset($vars['header_classes'][$field]['id'])) {
+        $vars['field_classes'][$field][$num]['headers'] = array($vars['header_classes'][$field]['id']);
+      }
 
       if (!empty($fields[$field]) && empty($fields[$field]->options['exclude'])) {
         $field_output = $handler->get_field($num, $field);