Index: wp-admin/async-upload.php
===================================================================
--- wp-admin/async-upload.php	(revision 28802)
+++ wp-admin/async-upload.php	(working copy)
@@ -43,7 +43,9 @@
 	send_nosniff_header();
 	nocache_headers();
 
-	wp_ajax_upload_attachment();
+	/** This action is documented in wp-admin/admin-ajax.php */
+	add_action( 'wp_ajax_upload-attachment', 'wp_ajax_upload_attachment', 1 );
+	do_action( 'wp_ajax_upload-attachment' );
 	die( '0' );
 }