diff --git a/policy_manager/variable.h b/policy_manager/variable.h
index 822ab3b..2c6a8e3 100644
--- a/policy_manager/variable.h
+++ b/policy_manager/variable.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_POLICY_MANAGER_VARIABLE_H
-#define CHROMEOS_PLATFORM_UPDATE_ENGINE_POLICY_MANAGER_VARIABLE_H
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_POLICY_MANAGER_VARIABLE_H_
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_POLICY_MANAGER_VARIABLE_H_
 
 #include <algorithm>
 #include <list>
@@ -165,4 +165,4 @@
 
 }  // namespace chromeos_policy_manager
 
-#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_POLICY_MANAGER_VARIABLE_H
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_POLICY_MANAGER_VARIABLE_H_