diff --git a/src/proto/vim9class.pro b/src/proto/vim9class.pro
index edbddd2..66c6107 100644
--- a/src/proto/vim9class.pro
+++ b/src/proto/vim9class.pro
@@ -6,7 +6,7 @@
 void ex_type(exarg_T *eap);
 int class_object_index(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int verbose);
 ufunc_T *find_class_func(char_u **arg);
-int class_member_exists(char_u *name, class_T **cl_ret, int *idx_ret, cctx_T *cctx);
+int class_member_index(char_u *name, size_t len, class_T **cl_ret, cctx_T *cctx);
 void copy_object(typval_T *from, typval_T *to);
 void object_unref(object_T *obj);
 void copy_class(typval_T *from, typval_T *to);