diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index b7e6f99..321ae9f 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -359,3 +359,6 @@
 
 # By default, disable SPMD Logical partitions
 ENABLE_SPMD_LP			:= 0
+
+# By default, disable PSA crypto (use MbedTLS legacy crypto API).
+PSA_CRYPTO			:= 0