Index: wp-includes/post-template.php
===================================================================
--- wp-includes/post-template.php	(revision 23299)
+++ wp-includes/post-template.php	(working copy)
@@ -1244,11 +1244,16 @@
  * @return bool False on failure, true if success.
  */
 function is_page_template( $template = '' ) {
-	if ( ! is_page() )
+	if ( ! is_page() && ! in_the_loop() ) {
 		return false;
+	} elseif ( in_the_loop() ) {
+		global $wp_the_query;
+		$page_template = get_page_template_slug( $wp_the_query->queried_object_id );
+	}
+	else {
+		$page_template = get_page_template_slug( get_queried_object_id() );
+	}
 
-	$page_template = get_page_template_slug( get_queried_object_id() );
-
 	if ( empty( $template ) )
 		return (bool) $page_template;