Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 18685)
+++ wp-includes/user.php	(working copy)
@@ -61,7 +61,7 @@
 	}
 
 	wp_set_auth_cookie($user->ID, $credentials['remember'], $secure_cookie);
-	do_action('wp_login', $credentials['user_login']);
+	do_action('wp_login', $user->user_login, $user);
 	return $user;
 }