diff --git a/secure_fw/partitions/ns_agent_mailbox/tfm_spe_mailbox.c b/secure_fw/partitions/ns_agent_mailbox/tfm_spe_mailbox.c
index 853d112..c288ca3 100644
--- a/secure_fw/partitions/ns_agent_mailbox/tfm_spe_mailbox.c
+++ b/secure_fw/partitions/ns_agent_mailbox/tfm_spe_mailbox.c
@@ -180,14 +180,14 @@
 {
     size_t in_len, out_len;
 
-    if ((params->psa_call_params.out_vec == NULL) ||
-        (params->psa_call_params.in_vec == NULL)) {
-        return MAILBOX_INVAL_PARAMS;
-    }
-
     in_len = params->psa_call_params.in_len;
     out_len = params->psa_call_params.out_len;
 
+    if (((params->psa_call_params.out_vec == NULL) && (out_len != 0)) ||
+        ((params->psa_call_params.in_vec == NULL) && (in_len != 0))) {
+        return MAILBOX_INVAL_PARAMS;
+    }
+
     if ((in_len > PSA_MAX_IOVEC) ||
         (out_len > PSA_MAX_IOVEC) ||
         ((in_len + out_len) > PSA_MAX_IOVEC)) {