diff --git a/examples/callbacks/sys.h b/examples/callbacks/sys.h
index e16ff964..126a1a28 100644
--- a/examples/callbacks/sys.h
+++ b/examples/callbacks/sys.h
@@ -1,3 +1,4 @@
 #include "cyclone/types.h"
 
 void start_c_thread(gc_thread_data *thd);
+object c_trampoline(gc_thread_data *parent_thd, object fnc, object arg);