diff --git a/dhcp_proxy_interface.h b/dhcp_proxy_interface.h
index 239095e..35636cf 100644
--- a/dhcp_proxy_interface.h
+++ b/dhcp_proxy_interface.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 SHILL_DHCP_PROXY_INTERFACE_
-#define SHILL_DHCP_PROXY_INTERFACE_
+#ifndef SHILL_DHCP_PROXY_INTERFACE_H_
+#define SHILL_DHCP_PROXY_INTERFACE_H_
 
 #include <string>
 
@@ -21,4 +21,4 @@
 
 }  // namespace shill
 
-#endif  // SHILL_DHCP_PROXY_INTERFACE_
+#endif  // SHILL_DHCP_PROXY_INTERFACE_H_