diff -rc htmlcxx-orig-0.85/html/tree.h htmlcxx-0.85/html/tree.h
*** htmlcxx-orig-0.85/html/tree.h	2015-09-02 13:57:17.988688798 +0200
--- htmlcxx-0.85/html/tree.h	2015-09-02 13:57:52.737768811 +0200
***************
*** 45,50 ****
--- 45,51 ----
  #ifndef tree_hh_
  #define tree_hh_
  
+ #include <cstddef>
  #include <cassert>
  #include <memory>
  #include <stdexcept>