--- a/include/libtorrent/config.hpp
+++ b/include/libtorrent/config.hpp
@@ -33,6 +33,8 @@ POSSIBILITY OF SUCH DAMAGE.
 #ifndef TORRENT_CONFIG_HPP_INCLUDED
 #define TORRENT_CONFIG_HPP_INCLUDED
 
+#include <cstddef>
+
 #include "libtorrent/aux_/disable_warnings_push.hpp"
 
 #define _FILE_OFFSET_BITS 64
--- a/include/libtorrent/ed25519.hpp
+++ b/include/libtorrent/ed25519.hpp
@@ -2,7 +2,7 @@
 #define ED25519_HPP
 
 #include "libtorrent/aux_/export.hpp" // for TORRENT_EXPORT
-#include <stddef.h> // for size_t
+#include <cstddef> // for ptrdiff_t, size_t
 
 namespace libtorrent {