diff --git a/mbox.h b/mbox.h
index 7ae002b..19d0a3f 100644
--- a/mbox.h
+++ b/mbox.h
@@ -130,6 +130,8 @@
 	struct mbox_msg msg;
 };
 
+struct mbox_context;
+
 typedef int (*mboxd_mbox_handler)(struct mbox_context *, union mbox_regs *,
 				  struct mbox_msg *);