diff --git a/lib/renderer/api/desktop-capturer.js b/lib/renderer/api/desktop-capturer.js
index 3b9e5a6505bc..ff47dfd8e987 100644
--- a/lib/renderer/api/desktop-capturer.js
+++ b/lib/renderer/api/desktop-capturer.js
@@ -3,7 +3,10 @@ const {ipcRenderer, nativeImage} = require('electron')
 const includes = [].includes
 let currentId = 0
 
-const incrementId = () => currentId += 1
+const incrementId = () => {
+  currentId += 1
+  return currentId
+}
 
 // |options.type| can not be empty and has to include 'window' or 'screen'.
 function isValid (options) {
@@ -27,7 +30,7 @@ exports.getSources = function (options, callback) {
   ipcRenderer.send('ELECTRON_BROWSER_DESKTOP_CAPTURER_GET_SOURCES', captureWindow, captureScreen, options.thumbnailSize, id)
   return ipcRenderer.once(`ELECTRON_RENDERER_DESKTOP_CAPTURER_RESULT_${id}`, (event, sources) => {
     callback(null, (() => {
-      results = []
+      const results = []
       sources.forEach(source => {
         results.push({
           id: source.id,