diff --git a/rialto/src/main.rs b/rialto/src/main.rs
index d9cffe0..0bdc927 100644
--- a/rialto/src/main.rs
+++ b/rialto/src/main.rs
@@ -37,7 +37,7 @@
 use hyp::{get_mem_sharer, get_mmio_guard};
 use libfdt::FdtError;
 use log::{debug, error, info};
-use service_vm_comm::{ServiceVmRequest, VmType};
+use service_vm_comm::{RequestProcessingError, Response, ServiceVmRequest, VmType};
 use service_vm_requests::process_request;
 use virtio_drivers::{
     device::socket::{VsockAddr, VMADDR_CID_HOST},
@@ -178,7 +178,15 @@
 
     let mut vsock_stream = VsockStream::new(socket_device, host_addr())?;
     while let ServiceVmRequest::Process(req) = vsock_stream.read_request()? {
-        let response = process_request(req, bcc_handover.as_ref());
+        let mut response = process_request(req, bcc_handover.as_ref());
+        // TODO(b/185878400): We don't want to issue a certificate to pVM when the client VM
+        // attestation is unfinished. The following code should be removed once the
+        // verification is completed.
+        if vm_type() == VmType::ProtectedVm
+            && matches!(response, Response::RequestClientVmAttestation(_))
+        {
+            response = Response::Err(RequestProcessingError::OperationUnimplemented);
+        }
         vsock_stream.write_response(&response)?;
         vsock_stream.flush()?;
     }