diff --git a/drivers/mailbox/k3-sec-proxy.c b/drivers/mailbox/k3-sec-proxy.c
index 88f3205..20fdb09 100644
--- a/drivers/mailbox/k3-sec-proxy.c
+++ b/drivers/mailbox/k3-sec-proxy.c
@@ -409,7 +409,7 @@
 	return 0;
 }
 
-static const u32 am6x_valid_threads[] = { 0, 1, 4, 5, 6, 7, 8, 9, 11, 12, 13 };
+static const u32 am6x_valid_threads[] = { 0, 1, 4, 5, 6, 7, 8, 9, 11, 12, 13, 20, 21, 22, 23 };
 
 static const struct k3_sec_proxy_desc am654_desc = {
 	.thread_count = 90,