diff --git a/lib/libxpc/include/xpc/msg.h b/lib/libxpc/include/xpc/msg.h
index 3ae443e..debd15c 100644
--- a/lib/libxpc/include/xpc/msg.h
+++ b/lib/libxpc/include/xpc/msg.h
@@ -39,7 +39,8 @@ extern kern_status_t xpc_msg_write(
 	const xpc_msg_t *msg,
 	size_t offset,
 	const void *p,
-	size_t count);
+	size_t count,
+	size_t *nr_written);
 
 extern kern_status_t xpc_msg_reply(
 	const xpc_msg_t *msg,
diff --git a/lib/libxpc/msg.c b/lib/libxpc/msg.c
index ec4b7d2..81d13c3 100644
--- a/lib/libxpc/msg.c
+++ b/lib/libxpc/msg.c
@@ -106,17 +106,17 @@ kern_status_t xpc_msg_write(
 	const xpc_msg_t *msg,
 	size_t offset,
 	const void *p,
-	size_t count)
+	size_t count,
+	size_t *nr_written)
 {
 	kern_iovec_t iov = IOVEC(p, count);
-	size_t w = 0;
 	return msg_write(
 		msg->msg_sender.e_channel,
 		msg->msg_sender.e_msg,
 		offset,
 		&iov,
 		1,
-		&w);
+		nr_written);
 }
 
 kern_status_t xpc_msg_reply(