diff --git a/include/boost/typeof/int_encoding.hpp b/include/boost/typeof/int_encoding.hpp
index 3984174..1f00d4f 100644
--- a/include/boost/typeof/int_encoding.hpp
+++ b/include/boost/typeof/int_encoding.hpp
@@ -7,6 +7,7 @@
 
 #include <boost/config.hpp>
 #include <boost/typeof/constant.hpp>
+#include <cstddef> // for std::size_t
 
 namespace boost { namespace type_of {
 
diff --git a/include/boost/typeof/typeof_impl.hpp b/include/boost/typeof/typeof_impl.hpp
index f5397e6..73a25df 100644
--- a/include/boost/typeof/typeof_impl.hpp
+++ b/include/boost/typeof/typeof_impl.hpp
@@ -12,6 +12,7 @@
 #include <boost/typeof/vector.hpp>
 #include <boost/type_traits/enable_if.hpp>
 #include <boost/type_traits/is_function.hpp>
+#include <cstddef> // for std::size_t
 
 #define BOOST_TYPEOF_VECTOR(n) BOOST_PP_CAT(boost::type_of::vector, n)