diff --git a/src/ints/xms.cpp b/src/ints/xms.cpp
index 10b53fc7..1d9d2af2 100644
--- a/src/ints/xms.cpp
+++ b/src/ints/xms.cpp
@@ -19,6 +19,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <stddef.h>
 #include "dosbox.h"
 #include "callback.h"
 #include "mem.h"