diff -Naur htmlcxx-0.85/html/tree.h htmlcxx-0.85/html/tree.h
--- htmlcxx-0.85/html/tree.h	2011-02-13 23:24:53.000000000 +0100
+++ htmlcxx-0.85/html/tree.h	2013-04-28 14:38:17.370643634 +0200
@@ -45,6 +45,7 @@
 #ifndef tree_hh_
 #define tree_hh_
 
+#include <cstddef>
 #include <cassert>
 #include <memory>
 #include <stdexcept>