diff --git a/facetapi.callbacks.inc b/facetapi.callbacks.inc
index b927ef1..e058fe7 100644
--- a/facetapi.callbacks.inc
+++ b/facetapi.callbacks.inc
@@ -38,7 +38,7 @@ function facetapi_map_bundle(array $values, array $options) {
 function facetapi_map_author(array $values) {
   $map = array();
   if (!empty($values)) {
-    $query = "SELECT u.uid AS uid, u.name AS name FROM {users} u WHERE u.uid IN " . db_placeholders($values);
+    $query = "SELECT u.uid AS uid, u.name AS name FROM {users} u WHERE u.uid IN (" . db_placeholders($values) . ")";
     $result = db_query($query, $values);
     while ($record = db_fetch_array($result)) {
       $map[$record['uid']] = $record['name'];