diff --git a/plat/arm/css/common/css_common.mk b/plat/arm/css/common/css_common.mk
index 29dd01d..984c1da 100644
--- a/plat/arm/css/common/css_common.mk
+++ b/plat/arm/css/common/css_common.mk
@@ -85,3 +85,12 @@
 # Process CSS_USE_SCMI_SDS_DRIVER flag
 $(eval $(call assert_boolean,CSS_USE_SCMI_SDS_DRIVER))
 $(eval $(call add_define,CSS_USE_SCMI_SDS_DRIVER))
+
+# Process CSS_NON_SECURE_UART flag
+# This undocumented build option is only to enable debug access to the UART
+# from non secure code, which is useful on some platforms.
+# Default (obviously) is off.
+CSS_NON_SECURE_UART		:= 0
+$(eval $(call assert_boolean,CSS_NON_SECURE_UART))
+$(eval $(call add_define,CSS_NON_SECURE_UART))
+