diff --git a/src/strings.c b/src/strings.c
index a87922d..98d420c 100644
--- a/src/strings.c
+++ b/src/strings.c
@@ -902,6 +902,12 @@
     if (rettv_list_alloc(rettv) == FAIL)
 	return;
 
+    if (in_vim9script()
+	    && (check_for_string_arg(argvars, 0) == FAIL
+		|| (argvars[1].v_type != VAR_UNKNOWN
+		    && check_for_bool_arg(argvars, 1) == FAIL)))
+	return;
+
     if (argvars[1].v_type != VAR_UNKNOWN)
 	utf8 = (int)tv_get_bool_chk(&argvars[1], NULL);
 
@@ -1108,6 +1114,12 @@
 {
     varnumber_T		skipcc = FALSE;
 
+    if (in_vim9script()
+	    && (check_for_string_arg(argvars, 0) == FAIL
+		|| (argvars[1].v_type != VAR_UNKNOWN
+		    && check_for_bool_arg(argvars, 1) == FAIL)))
+	return;
+
     if (argvars[1].v_type != VAR_UNKNOWN)
 	skipcc = tv_get_bool(&argvars[1]);
     if (skipcc < 0 || skipcc > 1)