diff --git a/src/list.c b/src/list.c
index 417f735..4b9236a 100644
--- a/src/list.c
+++ b/src/list.c
@@ -823,6 +823,11 @@
     long    maxdepth;
     int	    error = FALSE;
 
+    if (in_vim9script()
+	    && (check_for_list_arg(argvars, 0) == FAIL
+		|| check_for_opt_number_arg(argvars, 1) == FAIL))
+	return;
+
     if (argvars[0].v_type != VAR_LIST)
     {
 	semsg(_(e_listarg), "flatten()");
@@ -1267,6 +1272,11 @@
     garray_T	ga;
     char_u	*sep;
 
+    if (in_vim9script()
+	    && (check_for_list_arg(argvars, 0) == FAIL
+		|| check_for_opt_string_arg(argvars, 1) == FAIL))
+	return;
+
     if (argvars[0].v_type != VAR_LIST)
     {
 	emsg(_(e_listreq));
@@ -1470,6 +1480,12 @@
 
     rettv->v_type = VAR_STRING;
     rettv->vval.v_string = NULL;
+
+    if (in_vim9script()
+	    && (check_for_list_arg(argvars, 0) == FAIL
+		|| check_for_opt_bool_arg(argvars, 1) == FAIL))
+	return;
+
     if (argvars[0].v_type != VAR_LIST)
     {
 	emsg(_(e_invarg));
@@ -1522,6 +1538,12 @@
     int		error = FALSE;
     long	idx;
 
+    if (in_vim9script()
+	    && (check_for_list_arg(argvars, 0) == FAIL
+		|| check_for_number_arg(argvars, 1) == FAIL
+		|| check_for_opt_number_arg(argvars, 2) == FAIL))
+	return;
+
     if ((l = argvars[0].vval.v_list) == NULL
 			     || value_check_lock(l->lv_lock, arg_errmsg, TRUE))
 	return;
@@ -2489,6 +2511,16 @@
     int		ic = FALSE;
     int		error = FALSE;
 
+    if (in_vim9script()
+	    && ((argvars[0].v_type != VAR_STRING
+		    && argvars[0].v_type != VAR_LIST
+		    && argvars[0].v_type != VAR_DICT
+		    && check_for_string_arg(argvars, 0) == FAIL)
+		|| check_for_opt_bool_arg(argvars, 2) == FAIL
+		|| (argvars[2].v_type != VAR_UNKNOWN
+		    && check_for_opt_number_arg(argvars, 3) == FAIL)))
+	return;
+
     if (argvars[2].v_type != VAR_UNKNOWN)
 	ic = (int)tv_get_bool_chk(&argvars[2], &error);