diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index 53832c5..a211f66 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2016-2019, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2016-2020, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -201,6 +201,9 @@
 # Build option to choose whether Trusted Firmware uses library at ROM
 USE_ROMLIB			:= 0
 
+# Chain of trust.
+COT				:= tbbr
+
 # Use tbbr_oid.h instead of platform_oid.h
 USE_TBBR_DEFS			:= 1