diff --git a/include/boost/type_traits/array_traits.hpp b/include/boost/type_traits/array_traits.hpp
index 975f801..622c28f 100644
--- a/include/boost/type_traits/array_traits.hpp
+++ b/include/boost/type_traits/array_traits.hpp
@@ -9,6 +9,7 @@
 //
 #ifndef BOOST_TT_ARRAY_TRAITS_HPP
 # define BOOST_TT_ARRAY_TRAITS_HPP
+# include <cstddef>
 # include <boost/type_traits/utility.hpp>
 # include <boost/type_traits/ice.hpp>