http://bugs.gentoo.org/show_bug.cgi?id=366073
http://celestia.svn.sourceforge.net/viewvc/celestia?view=revision&revision=5178

Patch written by Nils Larsson <ni1s@nerdshack.com>
--- a/src/celengine/frametree.h
+++ b/src/celengine/frametree.h
@@ -14,6 +14,7 @@
 #define _CELENGINE_FRAMETREE_H_
 
 #include <vector>
+#include <cstddef>
 
 class Star;
 class Body;
