diff --git a/src/runtime/src/comms.rs b/src/runtime/src/comms.rs
index 67d8ddcc..8dfdfda9 100644
--- a/src/runtime/src/comms.rs
+++ b/src/runtime/src/comms.rs
@@ -147,7 +147,9 @@ async fn handle_connection(stream: &TcpStream, control: Rc<RefCell<kernel::Contr
                             break;
                         },
                         kernel::Message::RpcSend { is_async, data } => {
-                            debug!("RPC: is_async={} data={:?}", is_async, data);
+                            write_header(&stream, Reply::RPCRequest).await?;
+                            write_bool(&stream, is_async).await?;
+                            stream.send(data.iter().copied()).await?;
                         },
                         _ => {
                             error!("received unexpected message from core1 while kernel was running: {:?}", reply);
diff --git a/src/runtime/src/proto_async.rs b/src/runtime/src/proto_async.rs
index 95c24a30..3a35d7c6 100644
--- a/src/runtime/src/proto_async.rs
+++ b/src/runtime/src/proto_async.rs
@@ -84,6 +84,11 @@ pub async fn write_i8(stream: &TcpStream, value: i8) -> Result<()> {
     Ok(())
 }
 
+pub async fn write_bool(stream: &TcpStream, value: bool) -> Result<()> {
+    stream.send([value as u8].iter().copied()).await?;
+    Ok(())
+}
+
 pub async fn write_i32(stream: &TcpStream, value: i32) -> Result<()> {
     stream.send([
         (value >> 24) as u8,