diff --git a/index.ts b/index.ts
index 97a3fa4..4dfecde 100644
--- a/index.ts
+++ b/index.ts
@@ -642,7 +642,7 @@ 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
         }