diff --git a/gfx/ots/src/os2.cc b/gfx/ots/src/os2.cc
--- a/gfx/ots/src/os2.cc
+++ b/gfx/ots/src/os2.cc
@@ -1,12 +1,14 @@
 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // 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"
 
 // OS/2 - OS/2 and Windows Metrics
 // http://www.microsoft.com/opentype/otspec/os2.htm
 
 namespace ots {