diff --git a/src/proto/vim9script.pro b/src/proto/vim9script.pro
index 1b73e87..97c1c92 100644
--- a/src/proto/vim9script.pro
+++ b/src/proto/vim9script.pro
@@ -1,5 +1,6 @@
 /* vim9script.c */
 int in_vim9script(void);
+int in_old_script(int max_version);
 int current_script_is_vim9(void);
 void ex_vim9script(exarg_T *eap);
 int not_in_vim9(exarg_T *eap);