diff --git a/modules/comment/comment.install b/modules/comment/comment.install
index e5ac7d0..75decbf 100644
--- a/modules/comment/comment.install
+++ b/modules/comment/comment.install
@@ -66,6 +66,25 @@ function comment_update_6003() {
   return $ret;
 }
 
+/**
+ * @defgroup updates-6.x-extra Extra system updates for 6.x
+ * @{
+ */
+
+/**
+ * Add indices to uid fields.
+ */
+function comment_update_6004() {
+  $ret = array();
+  db_add_index($ret, 'comments', 'comment_uid', array('uid'));
+  db_add_index($ret, 'node_comment_statistics', 'last_comment_uid', array('last_comment_uid'));
+  return $ret;
+}
+
+/**
+ * @} End of "defgroup updates-6.x-extra"
+ * The next series of updates should start at 7000.
+ */
 
 /**
  * Implementation of hook_schema().
@@ -166,6 +185,7 @@ function comment_schema() {
     'indexes' => array(
       'pid'    => array('pid'),
       'nid'    => array('nid'),
+      'uid'    => array('comment_uid'),
       'status' => array('status'), // This index is probably unused
     ),
     'primary key' => array('cid'),
@@ -209,10 +229,10 @@ function comment_schema() {
     ),
     'primary key' => array('nid'),
     'indexes' => array(
-      'node_comment_timestamp' => array('last_comment_timestamp')
+      'node_comment_timestamp' => array('last_comment_timestamp'),
+      'last_comment_uid' => array('last_comment_uid'),
     ),
   );
 
   return $schema;
 }
-