diff --git a/oauth2/__init__.py b/oauth2/__init__.py
index 835270e3..736f3975 100644
--- a/oauth2/__init__.py
+++ b/oauth2/__init__.py
@@ -23,6 +23,7 @@
 """
 
 import base64
+import copy
 import urllib
 import time
 import random
@@ -642,6 +643,8 @@ def request(self, uri, method="GET", body='', headers=None,
 
         if not isinstance(headers, dict):
             headers = {}
+        else:
+            headers = copy.copy(headers)
 
         if method == "POST":
             headers['Content-Type'] = headers.get('Content-Type',