diff --git a/lib/get-certificate.js b/lib/get-certificate.js
index bf30192..926188d 100644
--- a/lib/get-certificate.js
+++ b/lib/get-certificate.js
@@ -235,7 +235,7 @@ module.exports.create = function (deps) {
         nextDomain();
       } else if (authz.status==='invalid') {
         unlink();
-        challengesState = authz.challenges.map(function (challenge) {
+        challengesState = (authz.challenges || []).map(function (challenge) {
           var result =  ' - ' + challenge.uri + ' [' + challenge.status + ']';
           if (challenge.error) {
             result += '\n   ' + challenge.error.detail;