diff --git a/includes/form.inc b/includes/form.inc
index c8d0ab7b59071406994c1013bbd9dac52ea541c8..e5d1b1b815bc180a09cbeb054c6a84e330f3857d 100644
--- a/includes/form.inc
+++ b/includes/form.inc
@@ -2788,9 +2788,14 @@ function theme_tableselect($variables) {
     // Add an empty header or a "Select all" checkbox to provide room for the
     // checkboxes/radios in the first table column.
     if ($element['#js_select']) {
+      // Add a "Select all" checkbox when checkboxes are displayed.
       drupal_add_js('misc/tableselect.js');
       array_unshift($header, array('class' => array('select-all')));
     }
+    else {
+      // Add an empty header when radio buttons are displayed.
+      array_unshift($header, '');
+    }
   }
   return theme('table', array('header' => $header, 'rows' => $rows, 'empty' => $element['#empty'], 'attributes' => $element['#attributes']));
 }