diff --git a/contrib/win32/win32compat/inc/unistd.h b/contrib/win32/win32compat/inc/unistd.h
index 874c30303..d1cca64f6 100644
--- a/contrib/win32/win32compat/inc/unistd.h
+++ b/contrib/win32/win32compat/inc/unistd.h
@@ -4,6 +4,7 @@
 * POSIX header and needed function definitions
 */
 #pragma once
+#include <stddef.h>
 #include "sys\types.h"
 #include "fcntl.h"