--- a/util/x509.lua	Tue Sep 10 18:16:11 2019 +0200
+++ b/util/x509.lua	Tue Sep 10 18:17:13 2019 +0200
@@ -238,7 +238,7 @@
 		local dn = subject[i];
 		if dn.oid == oid_commonname then
 			local name = nameprep(dn.value);
-			if name then
+			if name and idna_to_ascii(name) then
 				names[name] = true;
 			end
 		end