diff --git a/src/proto/vim9compile.pro b/src/proto/vim9compile.pro
index 03862a2..fb37923 100644
--- a/src/proto/vim9compile.pro
+++ b/src/proto/vim9compile.pro
@@ -3,6 +3,7 @@
 void clear_type_list(garray_T *gap);
 type_T *typval2type(typval_T *tv);
 int check_type(type_T *expected, type_T *actual, int give_msg);
+int check_argtype(type_T *expected, typval_T *actual_tv);
 int check_compare_types(exptype_T type, typval_T *tv1, typval_T *tv2);
 char_u *skip_type(char_u *start);
 type_T *parse_type(char_u **arg, garray_T *type_gap);