diff --git a/docs/api/app.md b/docs/api/app.md
index c93d383fa7444..aa277b0578487 100755
--- a/docs/api/app.md
+++ b/docs/api/app.md
@@ -987,7 +987,8 @@ let myWindow = null
 app.on('first-instance-ack', (event, additionalData) => {
   // Print out the ack received from the first instance.
   // Note this event handler must come before the requestSingleInstanceLock call.
-  console.log(additionalData)
+  // Expected output: '{"myAckKey":"myAckValue"}'
+  console.log(JSON.stringify(additionalData))
 })
 
 const additionalData = { myKey: 'myValue' }
@@ -1000,7 +1001,8 @@ if (!gotTheLock) {
     // We must call preventDefault if we're sending back data.
     event.preventDefault()
     // Print out data received from the second instance.
-    console.log(additionalData)
+    // Expected output: '{"myKey":"myValue"}'
+    console.log(JSON.stringify(additionalData))
 
     // Someone tried to run a second instance, we should focus our window.
     if (myWindow) {
diff --git a/spec-main/api-app-spec.ts b/spec-main/api-app-spec.ts
index b67bac74ad002..f774c97f7c29b 100644
--- a/spec-main/api-app-spec.ts
+++ b/spec-main/api-app-spec.ts
@@ -1,4 +1,4 @@
-import { expect } from 'chai';
+import { assert, expect } from 'chai';
 import * as cp from 'child_process';
 import * as https from 'https';
 import * as http from 'http';
@@ -315,13 +315,66 @@ describe('app module', () => {
       });
     });
 
-    it('sends and receives data', async () => {
+    it('sends and receives JSON object data', async () => {
       await testArgumentPassing({
         args: ['--send-ack', '--prevent-default', '--send-data'],
         expectedAdditionalData,
         expectedAck
       });
     });
+
+    it('sends and receives numerical data', async () => {
+      await testArgumentPassing({
+        args: ['--send-ack', '--ack-content=1', '--prevent-default', '--send-data', '--data-content=2'],
+        expectedAdditionalData: 2,
+        expectedAck: 1
+      });
+    });
+
+    it('sends and receives string data', async () => {
+      await testArgumentPassing({
+        args: ['--send-ack', '--ack-content="ack"', '--prevent-default', '--send-data', '--data-content="data"'],
+        expectedAdditionalData: 'data',
+        expectedAck: 'ack'
+      });
+    });
+
+    it('sends and receives boolean data', async () => {
+      await testArgumentPassing({
+        args: ['--send-ack', '--ack-content=true', '--prevent-default', '--send-data', '--data-content=false'],
+        expectedAdditionalData: false,
+        expectedAck: true
+      });
+    });
+
+    it('sends and receives array data', async () => {
+      await testArgumentPassing({
+        args: ['--send-ack', '--ack-content=[1, 2, 3]', '--prevent-default', '--send-data', '--data-content=[2, 3, 4]'],
+        expectedAdditionalData: [2, 3, 4],
+        expectedAck: [1, 2, 3]
+      });
+    });
+
+    it('sends and receives null data', async () => {
+      await testArgumentPassing({
+        args: ['--send-ack', '--ack-content=null', '--prevent-default', '--send-data', '--data-content=null'],
+        expectedAdditionalData: null,
+        expectedAck: null
+      });
+    });
+
+    it('cannot send or receive undefined data', async () => {
+      try {
+        await testArgumentPassing({
+          args: ['--send-ack', '--ack-content="undefined"', '--prevent-default', '--send-data', '--data-content="undefined"'],
+          expectedAdditionalData: undefined,
+          expectedAck: undefined
+        });
+        assert(false);
+      } catch (e) {
+        // This is expected.
+      }
+    });
   });
 
   describe('app.relaunch', () => {
diff --git a/spec/fixtures/api/singleton-data/main.js b/spec/fixtures/api/singleton-data/main.js
index e1ba175f3669a..f79ed9ccc9bce 100644
--- a/spec/fixtures/api/singleton-data/main.js
+++ b/spec/fixtures/api/singleton-data/main.js
@@ -13,7 +13,7 @@ const preventDefault = app.commandLine.hasSwitch('prevent-default');
 // Send an object back for the ack rather than undefined.
 const sendAck = app.commandLine.hasSwitch('send-ack');
 
-const obj = {
+let obj = {
   level: 1,
   testkey: 'testvalue1',
   inner: {
@@ -21,7 +21,7 @@ const obj = {
     testkey: 'testvalue2'
   }
 };
-const ackObj = {
+let ackObj = {
   level: 1,
   testkey: 'acktestvalue1',
   inner: {
@@ -30,6 +30,19 @@ const ackObj = {
   }
 };
 
+if (app.commandLine.hasSwitch('data-content')) {
+  obj = JSON.parse(app.commandLine.getSwitchValue('data-content'));
+  if (obj === 'undefined') {
+    obj = undefined;
+  }
+}
+if (app.commandLine.hasSwitch('ack-content')) {
+  ackObj = JSON.parse(app.commandLine.getSwitchValue('ack-content'));
+  if (ackObj === 'undefined') {
+    ackObj = undefined;
+  }
+}
+
 app.on('first-instance-ack', (event, additionalData) => {
   console.log(JSON.stringify(additionalData));
 });