diff --git a/mailbox/CMakeLists.txt b/mailbox/CMakeLists.txt
index 44d8c82..a3bc60f 100644
--- a/mailbox/CMakeLists.txt
+++ b/mailbox/CMakeLists.txt
@@ -1,5 +1,6 @@
 #
-# Copyright (c) 2020-2022 Arm Limited.
+# SPDX-FileCopyrightText: Copyright 2020-2023 Arm Limited and/or its affiliates <open-source-office@arm.com>
+# SPDX-License-Identifier: GPL-2.0-only
 #
 # This program is free software and is provided to you under the terms of the
 # GNU General Public License version 2 as published by the Free Software
@@ -15,8 +16,6 @@
 # along with this program; if not, you can access it online at
 # http://www.gnu.org/licenses/gpl-2.0.html.
 #
-# SPDX-License-Identifier: GPL-2.0-only
-#
 
 cmake_minimum_required(VERSION 3.0.2)
 
@@ -39,7 +38,7 @@
 # Build the kernel module
 add_custom_target(mailbox-module ALL
     COMMAND ${CMAKE_MAKE_PROGRAM} -C ${KDIR}
-                  M=${CMAKE_CURRENT_SOURCE_DIR} CONFIG_ARM_MHU_V2=m CONFIG_ARM_MHU=m
+                  C=2 M=${CMAKE_CURRENT_SOURCE_DIR} CONFIG_ARM_MHU_V2=m CONFIG_ARM_MHU=m
                   CROSS_COMPILE=${CROSS_COMPILE} ARCH=${ARCH} modules
                   BYPRODUCTS
                   ${CMAKE_CURRENT_SOURCE_DIR}/arm_mhu.ko
@@ -57,4 +56,4 @@
                   COMMENT "Building arm_mhu.ko arm_mhu_v2.ko"
                   VERBATIM)
 
-install(FILES arm_mhu.ko arm_mhu_v2.ko DESTINATION "modules")
\ No newline at end of file
+install(FILES arm_mhu.ko arm_mhu_v2.ko DESTINATION "modules")