--- a/mozilla/gfx/ots/src/os2.cc
+++ b/mozilla/gfx/ots/src/os2.cc
@@ -2,6 +2,8 @@
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
+#include <cstddef>
+
#include "os2.h"
#include "head.h"