diff --git a/index.d.ts b/index.d.ts
index 0e2b0fd..4c7b53e 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -17,7 +17,8 @@ export interface AxiosProxyConfig {
   auth?: {
     username: string;
     password:string;
-  }
+  };
+  protocol?: string;
 }
 
 export type Method = 
diff --git a/lib/adapters/http.js b/lib/adapters/http.js
index 8fc9e40..8225f00 100755
--- a/lib/adapters/http.js
+++ b/lib/adapters/http.js
@@ -13,6 +13,8 @@ var pkg = require('./../../package.json');
 var createError = require('../core/createError');
 var enhanceError = require('../core/enhanceError');
 
+var isHttps = /https:?/;
+
 /*eslint consistent-return:0*/
 module.exports = function httpAdapter(config) {
   return new Promise(function dispatchHttpRequest(resolvePromise, rejectPromise) {
@@ -76,8 +78,8 @@ module.exports = function httpAdapter(config) {
       delete headers.Authorization;
     }
 
-    var isHttps = protocol === 'https:';
-    var agent = isHttps ? config.httpsAgent : config.httpAgent;
+    var isHttpsRequest = isHttps.test(protocol);
+    var agent = isHttpsRequest ? config.httpsAgent : config.httpAgent;
 
     var options = {
       path: buildURL(parsed.path, config.params, config.paramsSerializer).replace(/^\?/, ''),
@@ -130,15 +132,16 @@ module.exports = function httpAdapter(config) {
     }
 
     var transport;
+    var isHttpsProxy = isHttpsRequest && (proxy ? isHttps.test(proxy.protocol) : true);
     if (config.transport) {
       transport = config.transport;
     } else if (config.maxRedirects === 0) {
-      transport = isHttps ? https : http;
+      transport = isHttpsProxy ? https : http;
     } else {
       if (config.maxRedirects) {
         options.maxRedirects = config.maxRedirects;
       }
-      transport = isHttps ? httpsFollow : httpFollow;
+      transport = isHttpsProxy ? httpsFollow : httpFollow;
     }
 
     if (config.maxContentLength && config.maxContentLength > -1) {