diff --git a/mbv/apps/timer/timer.cc b/mbv/apps/timer/timer.cc
index 4f50025..5ea3002 100644
--- a/mbv/apps/timer/timer.cc
+++ b/mbv/apps/timer/timer.cc
@@ -5,6 +5,10 @@
 #include "pol0.h"
 #include "timer.h"
 
+extern "C" {
+void BiosWozmon();
+}
+
 namespace {
 
 struct Gpio {