diff --git a/src/core.js b/src/core.js
index a34954ab1..ae0f97231 100644
--- a/src/core.js
+++ b/src/core.js
@@ -33,8 +33,9 @@ function getPdf(arg, callback) {
   var xhr = new XMLHttpRequest();
   xhr.open('GET', params.url);
   xhr.mozResponseType = xhr.responseType = 'arraybuffer';
-  xhr.expected = (params.url.indexOf('http:') === 0 ||
-                  params.url.indexOf('https:') === 0) ? 200 : 0;
+  var protocol = params.url.indexOf(':') < 0 ? window.location.protocol :
+    params.url.substring(0, params.url.indexOf(':') + 1);
+  xhr.expected = (protocol === 'http:' || protocol === 'https:') ? 200 : 0;
 
   if ('progress' in params)
     xhr.onprogress = params.progress || undefined;