diff --git a/src/util/request-manager.js b/src/util/request-manager.js
index 8b2226ae6a..eda4b5969a 100644
--- a/src/util/request-manager.js
+++ b/src/util/request-manager.js
@@ -433,9 +433,7 @@ export default class RequestManager {
           }
         }
 
-        const server = res.caseless.get('server');
-
-        if (res.statusCode === 401 && server === 'GitHub.com') {
+        if (res.statusCode === 401 && res.caseless && res.caseless.get('server') === 'GitHub.com') {
           const message = `${res.body.message}. If using GITHUB_TOKEN in your env, check that it is valid.`;
           rejectWithoutUrl(new Error(this.reporter.lang('unauthorizedResponse', server, message)));
         }