diff --git a/sys/netlink/netlink_message_writer.h b/sys/netlink/netlink_message_writer.h
--- a/sys/netlink/netlink_message_writer.h
+++ b/sys/netlink/netlink_message_writer.h
@@ -50,7 +50,7 @@
 	nl_writer_cb		*cb;		/* Callback to flush data */
 	union {
 		void		*arg_ptr;	/* Callback argument as pointer */
-		uint64_t	arg_uint;	/* Callback argument as int */
+		uintptr_t	arg_uint;	/* Callback argument as int */
 	};
 	int			num_messages;	/* Number of messages in the buffer */
 	int			malloc_flag;	/* M_WAITOK or M_NOWAIT */
diff --git a/sys/netlink/netlink_message_writer.c b/sys/netlink/netlink_message_writer.c
--- a/sys/netlink/netlink_message_writer.c
+++ b/sys/netlink/netlink_message_writer.c
@@ -451,7 +451,7 @@
 {
 	if (!nlmsg_get_buf(nw, size, false, false))
 		return (false);
-	nw->arg_uint = (uint64_t)protocol << 16 | (uint64_t)group_id;
+	nw->arg_uint = (uintptr_t)protocol << 16 | (uintptr_t)group_id;
 	nw->writer_target = NS_WRITER_TARGET_GROUP;
 	nlmsg_set_callback(nw);
 	return (true);