diff --git a/search_api.admin.inc b/search_api.admin.inc
index df0816b..134cfd9 100644
--- a/search_api.admin.inc
+++ b/search_api.admin.inc
@@ -1488,7 +1488,7 @@ function search_api_admin_index_fields(array $form, array &$form_state, SearchAp
   $form['description'] = array(
     '#type' => 'item',
     '#title' => t('Select fields to index'),
-    '#description' => t('<p>The datatype of a field determines how it can be used for searching and filtering. ' .
+    '#description' => t('<p>The datatype of a field determines how it can be used for searching and filtering. Fields indexed with type "Fulltext" and multi-valued fields (marked with <sup>1</sup>) cannot be used for sorting. ' .
         'The boost is used to give additional weight to certain fields, e.g. titles or tags. It only takes effect for fulltext fields.</p>' .
         '<p>Whether detailed field types are supported depends on the type of server this index resides on. ' .
         'In any case, fields of type "Fulltext" will always be fulltext-searchable.</p>'),
@@ -1499,6 +1499,10 @@ function search_api_admin_index_fields(array $form, array &$form_state, SearchAp
   }
   foreach ($fields as $key => $info) {
     $form['fields'][$key]['title']['#markup'] = check_plain($info['name']);
+    if (search_api_is_list_type($info['type'])) {
+      $form['fields'][$key]['title']['#markup'] .= ' <sup><a href="#note-multi-valued" class="note-ref">1</a></sup>';
+      $multi_valued_field_present = TRUE;
+    }
     $form['fields'][$key]['machine_name']['#markup'] = check_plain($key);
     if (isset($info['description'])) {
       $form['fields'][$key]['description'] = array(
@@ -1588,6 +1592,10 @@ function search_api_admin_index_fields(array $form, array &$form_state, SearchAp
     }
   }
 
+  if (!empty($multi_valued_field_present)) {
+    $form['note']['#markup'] = '<div id="note-multi-valued"><small><sup>1</sup> ' . t('Multi-valued field') . '</small></div>';
+  }
+
   $form['submit'] = array(
     '#type' => 'submit',
     '#value' => t('Save changes'),
@@ -1767,11 +1775,13 @@ function theme_search_api_admin_fields_table($variables) {
     }
   }
 
+  $note = isset($form['note']) ? $form['note'] : '';
   $submit = $form['submit'];
   $additional = isset($form['additional']) ? $form['additional'] : FALSE;
-  unset($form['submit'], $form['additional']);
+  unset($form['note'], $form['submit'], $form['additional']);
   $output = drupal_render_children($form);
   $output .= theme('table', array('header' => $header, 'rows' => $rows));
+  $output .= render($note);
   $output .= render($submit);
   if ($additional) {
     $output .= render($additional);