diff --git a/a8/types.h b/a8/types.h
index c947814..1122210 100644
--- a/a8/types.h
+++ b/a8/types.h
@@ -4,6 +4,7 @@
 namespace a8
 {
     typedef long long tick_t;
+    struct XTimerPtr;
 
     struct SendQueueNode
     {