https://bugs.gentoo.org/890361
--- a/src/level_game.cpp
+++ b/src/level_game.cpp
@@ -27,6 +27,8 @@
 
 #include "portability.h"
 
+#include <cassert>
+#include <cstddef>
 #ifdef LINUX
 #include <endian.h>
 #endif // LINUX
--- a/src/level_game.h
+++ b/src/level_game.h
@@ -28,6 +28,7 @@
 #ifndef __LEVEL_GAME_H__
 #define __LEVEL_GAME_H__
 
+#include <cassert>
 #include <time.h>
 #include "stack.h"