diff --git a/utils/invalid-domains.json b/utils/invalid-domains.json
index 4c49294bee..45599ab2ec 100644
--- a/utils/invalid-domains.json
+++ b/utils/invalid-domains.json
@@ -5,6 +5,7 @@
   "noreply",
   "notifications",
   "notification",
+  "_acme-challenge",
   "ww1",
   "ww2",
   "ww3",