diff --git a/include/common/hathreads.h b/include/common/hathreads.h
index 2620b77..15b8ce2 100644
--- a/include/common/hathreads.h
+++ b/include/common/hathreads.h
@@ -866,4 +866,7 @@
 	__asm __volatile("" ::: "memory");
 }
 
+/* Dummy I/O handler used by the sync pipe.*/
+void thread_sync_io_handler(int fd);
+
 #endif /* _COMMON_HATHREADS_H */