diff --git a/src/fold.c b/src/fold.c
index f10294d..d9cba6a 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -3658,6 +3658,9 @@
     linenr_T	lnum;
     linenr_T	first, last;
 
+    if (in_vim9script() && check_for_lnum_arg(argvars, 0) == FAIL)
+	return;
+
     lnum = tv_get_lnum(argvars);
     if (lnum >= 1 && lnum <= curbuf->b_ml.ml_line_count)
     {
@@ -3701,6 +3704,9 @@
 # ifdef FEAT_FOLDING
     linenr_T	lnum;
 
+    if (in_vim9script() && check_for_lnum_arg(argvars, 0) == FAIL)
+	return;
+
     lnum = tv_get_lnum(argvars);
     if (lnum >= 1 && lnum <= curbuf->b_ml.ml_line_count)
 	rettv->vval.v_number = foldLevel(lnum);
@@ -3789,6 +3795,10 @@
 
     rettv->v_type = VAR_STRING;
     rettv->vval.v_string = NULL;
+
+    if (in_vim9script() && check_for_lnum_arg(argvars, 0) == FAIL)
+	return;
+
 # ifdef FEAT_FOLDING
     if (entered)
 	return; // reject recursive use