diff --git a/src/proto/evalvars.pro b/src/proto/evalvars.pro
index a108310..43c2528 100644
--- a/src/proto/evalvars.pro
+++ b/src/proto/evalvars.pro
@@ -88,5 +88,6 @@
 callback_T get_callback(typval_T *arg);
 void put_callback(callback_T *cb, typval_T *tv);
 void set_callback(callback_T *dest, callback_T *src);
+void copy_callback(callback_T *dest, callback_T *src);
 void free_callback(callback_T *callback);
 /* vim: set ft=c : */