diff --git a/src/proto/vim9class.pro b/src/proto/vim9class.pro
index 74d33c0..13a643d 100644
--- a/src/proto/vim9class.pro
+++ b/src/proto/vim9class.pro
@@ -7,6 +7,7 @@
 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_index(char_u *name, size_t len, class_T **cl_ret, cctx_T *cctx);
+int inside_class(cctx_T *cctx_arg, class_T *cl);
 void copy_object(typval_T *from, typval_T *to);
 void object_unref(object_T *obj);
 void copy_class(typval_T *from, typval_T *to);