diff --git a/verifier/app.js b/verifier/app.js
index f6f779078fabbd3a723956aabb29577310af4ce2..d6d7a52aa0a038b56799a08f75afaff18c130518 100644
--- a/verifier/app.js
+++ b/verifier/app.js
@@ -82,7 +82,7 @@ function doVerify(req, resp, next) {
       });
     },
     function(error) {
-      resp.json({"status":"failure", reason: error.toString()});
+      resp.json({"status":"failure", reason: (error ? error.toString() : "unknown")});
       metrics.report('verify', {
         result: 'failure',
         rp: audience