diff --git comment_revisions.install comment_revisions.install
index b0d753e..6e02782 100644
--- comment_revisions.install
+++ comment_revisions.install
@@ -61,7 +61,12 @@ function comment_revisions_schema() {
         'default' => 0,
         'description' => t('The revision was made by the user.')
       )
-    ), 'primary key' => array('vid'), 'unique key' => array( 'rid' => array('vid'))
+    ),
+    'primary key' => array('vid'),
+    'indexes' => array(
+      'cid' => array('cid', 'vid'),
+    ),
+    'unique key' => array( 'rid' => array('vid'))
   );
 
   $schema['comment_revisions_actual'] = array(
@@ -124,3 +129,12 @@ function comment_revisions_update_6000() {
   drupal_set_message('Be sure to check Comment Revisions role permissions, as some permission options have changed.');
   return $ret;
 }
+
+/**
+ * 6001: Add cid index to {comment_revisions}.
+ */
+function comment_revisions_update_6001() {
+  $ret = array();
+  db_add_index($ret, 'comment_revisions', 'cid', array('cid', 'vid'));
+  return $ret;
+}