diff --git a/lib/plugins/authentication/before-request.js b/lib/plugins/authentication/before-request.js
index b6152d67..6bf2fdbc 100644
--- a/lib/plugins/authentication/before-request.js
+++ b/lib/plugins/authentication/before-request.js
@@ -1,6 +1,7 @@
 module.exports = authenticationBeforeRequest
 
 const btoa = require('btoa-lite')
+const uniq = require('lodash/uniq')
 
 function authenticationBeforeRequest (state, options) {
   if (!state.auth.type) {
@@ -26,7 +27,9 @@ function authenticationBeforeRequest (state, options) {
 
   if (state.auth.type === 'app') {
     options.headers['authorization'] = `Bearer ${state.auth.token}`
-    options.headers['accept'] = 'application/vnd.github.machine-man-preview+json'
+    const acceptHeaders = options.headers['accept'].split(',')
+      .concat('application/vnd.github.machine-man-preview+json')
+    options.headers['accept'] = uniq(acceptHeaders).filter(Boolean).join(',')
     return
   }