diff --git a/src/vm.c b/src/vm.c
index 2cc8412ad..31e1e4bd1 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -394,10 +394,9 @@ mrb_funcall_id(mrb_state *mrb, mrb_value self, mrb_sym mid, mrb_int argc, ...)
 }
 
 static mrb_int
-mrb_ci_kidx(mrb_callinfo *ci)
+mrb_ci_kidx(const mrb_callinfo *ci)
 {
-  if (ci->nk == 0) return -1;
-  return (ci->n % 14) + 1;
+  return (ci->n == CALL_MAXARGS) ? 2 : ci->n + 1;
 }
 
 static mrb_int