diff --git a/src/sign.c b/src/sign.c
index fd373b5..bd8cb6c 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -2274,7 +2274,11 @@
 	return;
 
     if (argvars[0].v_type != VAR_UNKNOWN)
+    {
+	if (in_vim9script() && check_for_string_arg(argvars, 0) == FAIL)
+	    return;
 	name = tv_get_string(&argvars[0]);
+    }
 
     sign_getlist(name, rettv->vval.v_list);
 }