diff --git a/lib/XMLHttpRequest.js b/lib/XMLHttpRequest.js
index 4893913..7551057 100644
--- a/lib/XMLHttpRequest.js
+++ b/lib/XMLHttpRequest.js
@@ -425,7 +425,7 @@ exports.XMLHttpRequest = function() {
           return;
         }
 
-        response.setEncoding("utf8");
+        if (response.setEncoding) response.setEncoding("utf8");
 
         setState(self.HEADERS_RECEIVED);
         self.status = response.statusCode;