diff --git a/extent_writer.h b/extent_writer.h
index 1bb6f4a..1b38ae6 100644
--- a/extent_writer.h
+++ b/extent_writer.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_EXTENT_WRITER_H__
-#define CHROMEOS_PLATFORM_UPDATE_ENGINE_EXTENT_WRITER_H__
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_EXTENT_WRITER_H_
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_EXTENT_WRITER_H_
 
 #include <vector>
 #include "base/logging.h"
@@ -118,4 +118,4 @@
 
 }  // namespace chromeos_update_engine
 
-#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_EXTENT_WRITER_H__
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_EXTENT_WRITER_H_