diff --git a/meta-digi-arm/conf/machine/ccmp15-dvk.conf b/meta-digi-arm/conf/machine/ccmp15-dvk.conf
index 438b46414..9d23122e2 100644
--- a/meta-digi-arm/conf/machine/ccmp15-dvk.conf
+++ b/meta-digi-arm/conf/machine/ccmp15-dvk.conf
@@ -168,6 +168,9 @@ BOOTABLE_ARTIFACTS = " \
 # TRUSTFENCE basic support
 # Alternatively, uncommment to enable the console with the specified GPIO
 # TRUSTFENCE_CONSOLE_GPIO_ENABLE_NAME ?= "GPIOB6"
+#
+# The CCMP15 can only use key 0. This setting cannot be overriden.
+TRUSTFENCE_KEY_INDEX = "0"
 
 # Default overlayfs_etc mount point and type
 OVERLAYFS_ETC_MOUNT_POINT ?= "/mnt/data"