--- xnu/xnu-792/iokit/Kernel/IOStringFuncs.c
+++ xnu/xnu-201.5/iokit/Kernel/IOStringFuncs.c
@@ -71,6 +71,7 @@
 #include <limits.h>
 */
 #include <sys/types.h>
+#include <stddef.h>
 #include <machine/limits.h>
 
 typedef int BOOL;