diff --git a/src/undo.c b/src/undo.c
index 171e817..8141301 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -3646,6 +3646,9 @@
     void
 f_undofile(typval_T *argvars UNUSED, typval_T *rettv)
 {
+    if (in_vim9script() && check_for_string_arg(argvars, 0) == FAIL)
+	return;
+
     rettv->v_type = VAR_STRING;
 #ifdef FEAT_PERSISTENT_UNDO
     {