diff --git a/__tests__/proxy.test.ts b/__tests__/proxy.test.ts
index e8e79f4..7ba3cef 100644
--- a/__tests__/proxy.test.ts
+++ b/__tests__/proxy.test.ts
@@ -2,6 +2,7 @@ import * as http from 'http'
 import * as httpm from '../_out'
 import * as pm from '../_out/proxy'
 import * as proxy from 'proxy'
+import * as tunnelm from 'tunnel'
 
 let _proxyConnects: string[]
 let _proxyServer: http.Server
@@ -195,6 +196,26 @@ describe('proxy', () => {
     expect(obj.url).toBe('https://httpbin.org/get')
     expect(_proxyConnects).toHaveLength(0)
   })
+
+  it('proxyAuth not set in tunnel agent when authentication is not provided', async () => {
+    process.env['https_proxy'] = 'http://127.0.0.1:8080'
+    const httpClient = new httpm.HttpClient()
+    let agent: tunnelm.TunnelingAgent = httpClient.getAgent('https://some-url')
+    console.log(agent)
+    expect(agent.proxyOptions.host).toBe('127.0.0.1')
+    expect(agent.proxyOptions.port).toBe('8080')
+    expect(agent.proxyOptions.proxyAuth).toBe(undefined)
+  })
+
+  it('proxyAuth is set in tunnel agent when authentication is provided', async () => {
+    process.env['https_proxy'] = 'http://user:password@127.0.0.1:8080'
+    const httpClient = new httpm.HttpClient()
+    let agent: tunnelm.TunnelingAgent = httpClient.getAgent('https://some-url')
+    console.log(agent)
+    expect(agent.proxyOptions.host).toBe('127.0.0.1')
+    expect(agent.proxyOptions.port).toBe('8080')
+    expect(agent.proxyOptions.proxyAuth).toBe('user:password')
+  })
 })
 
 function _clearVars() {
diff --git a/index.ts b/index.ts
index 97a3fa4..a7858d9 100644
--- a/index.ts
+++ b/index.ts
@@ -642,7 +642,9 @@ export class HttpClient {
         maxSockets: maxSockets,
         keepAlive: this._keepAlive,
         proxy: {
-          proxyAuth: `${proxyUrl.username}:${proxyUrl.password}`,
+          ...((proxyUrl.username || proxyUrl.password) && {
+            proxyAuth: `${proxyUrl.username}:${proxyUrl.password}`
+          }),
           host: proxyUrl.hostname,
           port: proxyUrl.port
         }