diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index ea22655..57529ee 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -150,6 +150,10 @@
 # Enable Handoff protocol using transfer lists
 TRANSFER_LIST			:= 0
 
+# Enables support for the gcc compiler option "-mharden-sls=all".
+# By default, disables all SLS hardening.
+HARDEN_SLS			:= 0
+
 # Secure hash algorithm flag, accepts 3 values: sha256, sha384 and sha512.
 # The default value is sha256.
 HASH_ALG			:= sha256