diff --git a/src/proto/vim9compile.pro b/src/proto/vim9compile.pro
index 410910f..4f2fffe 100644
--- a/src/proto/vim9compile.pro
+++ b/src/proto/vim9compile.pro
@@ -1,6 +1,6 @@
 /* vim9compile.c */
 int script_var_exists(char_u *name, size_t len, int vim9script, cctx_T *cctx);
-int check_defined(char_u *p, size_t len, cctx_T *cctx);
+int check_defined(char_u *p, size_t len, cctx_T *cctx, int is_arg);
 int check_compare_types(exprtype_T type, typval_T *tv1, typval_T *tv2);
 int use_typecheck(type_T *actual, type_T *expected);
 int need_type(type_T *actual, type_T *expected, int offset, int arg_idx, cctx_T *cctx, int silent, int actual_is_const);