Index: wp-includes/template.php
===================================================================
--- wp-includes/template.php	(revision 21259)
+++ wp-includes/template.php	(working copy)
@@ -21,7 +21,7 @@
  * @return string Full path to file.
  */
 function get_query_template( $type, $templates = array() ) {
-	$type = preg_replace( '|[^a-z0-9-]+|', '', $type );
+	$type = preg_replace( '|[^a-z0-9-_]+|', '', $type );
 
 	if ( empty( $templates ) )
 		$templates = array("{$type}.php");