diff --git a/kernel/ethosu_mailbox.h b/kernel/ethosu_mailbox.h
index a3e2c14..c4c71a9 100644
--- a/kernel/ethosu_mailbox.h
+++ b/kernel/ethosu_mailbox.h
@@ -28,7 +28,7 @@
 
 #include <linux/types.h>
 #include <linux/mailbox_client.h>
-#include <linux/workqueue.h>
+#include <linux/wait.h>
 #include <linux/idr.h>
 
 /****************************************************************************
@@ -48,6 +48,8 @@
 	struct device         *dev;
 	struct rpmsg_endpoint *ept;
 	struct idr            msg_idr;
+	atomic_t              done;
+	wait_queue_head_t     send_queue;
 };
 
 /**