diff --git a/iommu_ref_model/libiommu/src/iommu_ats.c b/iommu_ref_model/libiommu/src/iommu_ats.c
index dc9625e3..21123a08 100644
--- a/iommu_ref_model/libiommu/src/iommu_ats.c
+++ b/iommu_ref_model/libiommu/src/iommu_ats.c
@@ -147,15 +147,17 @@ handle_page_request(
     //    a. `ddtp.iommu_mode` is `2LVL` and `DDI[2]` is not 0
     //    b. `ddtp.iommu_mode` is `1LVL` and either `DDI[2]` is not 0 or `DDI[1]` is not 0
     if ( g_reg_file.ddtp.iommu_mode == DDT_2LVL && DDI[2] != 0 ) {
-        report_fault(260, PAGE_REQ_MSG_CODE, 0, PCIE_MESSAGE_REQUEST, 0,
+        cause = 260; // "Transaction type disallowed"
+        report_fault(cause, PAGE_REQ_MSG_CODE, 0, PCIE_MESSAGE_REQUEST, 0,
                      device_id, pr->PV, pr->PID, pr->PRIV);
-        response_code = RESPONSE_FAILURE;
+        response_code = INVALID_REQUEST;
         goto send_prgr;
     }
     if ( g_reg_file.ddtp.iommu_mode == DDT_1LVL && (DDI[2] != 0 || DDI[1] != 0) ) {
-        report_fault(260, PAGE_REQ_MSG_CODE, 0, PCIE_MESSAGE_REQUEST, 0,
+        cause = 260; // "Transaction type disallowed"
+        report_fault(cause, PAGE_REQ_MSG_CODE, 0, PCIE_MESSAGE_REQUEST, 0,
                      device_id, pr->PV, pr->PID, pr->PRIV);
-        response_code = RESPONSE_FAILURE;
+        response_code = INVALID_REQUEST;
         goto send_prgr;
     }
     // To process a "Page Request" or "Stop Marker" message, the IOMMU first
diff --git a/iommu_ref_model/test/test_app.c b/iommu_ref_model/test/test_app.c
index 3666ef13..9163c41b 100644
--- a/iommu_ref_model/test/test_app.c
+++ b/iommu_ref_model/test/test_app.c
@@ -204,7 +204,7 @@ main(void) {
     exp_msg.EXEC_REQ = 0;
     exp_msg.DSV = 1;
     exp_msg.DSEG = 0x43;
-    exp_msg.PAYLOAD = (0x1234UL << 48UL) | (RESPONSE_FAILURE << 44UL);
+    exp_msg.PAYLOAD = (0x1234UL << 48UL) | (INVALID_REQUEST << 44UL);
     handle_page_request(&pr);
     fail_if( ( exp_msg_received == 0 ) );
     fail_if( ( check_msg_faults(260, pr.PV, pr.PID, pr.PRIV, 0x431234, PAGE_REQ_MSG_CODE) < 0 ) );
@@ -233,7 +233,7 @@ main(void) {
     exp_msg.EXEC_REQ = 0;
     exp_msg.DSV = 1;
     exp_msg.DSEG = 0x43;
-    exp_msg.PAYLOAD = (0x1234UL << 48UL) | (RESPONSE_FAILURE << 44UL);
+    exp_msg.PAYLOAD = (0x1234UL << 48UL) | (INVALID_REQUEST << 44UL);
     handle_page_request(&pr);
     fail_if( ( exp_msg_received == 0 ) );
     fail_if( ( check_msg_faults(260, pr.PV, pr.PID, pr.PRIV, 0x431234, PAGE_REQ_MSG_CODE) < 0 ) );
@@ -259,7 +259,7 @@ main(void) {
     exp_msg.EXEC_REQ = 0;
     exp_msg.DSV = 1;
     exp_msg.DSEG = 0x43;
-    exp_msg.PAYLOAD = (0x1234UL << 48UL) | (RESPONSE_FAILURE << 44UL);
+    exp_msg.PAYLOAD = (0x1234UL << 48UL) | (INVALID_REQUEST << 44UL);
     handle_page_request(&pr);
     fail_if( ( exp_msg_received == 0 ) );
     fail_if( ( check_msg_faults(260, pr.PV, pr.PID, pr.PRIV, 0x431234, PAGE_REQ_MSG_CODE) < 0 ) );