diff --git a/requests/structures.py b/requests/structures.py
index 3e5f2faa..edbe3f5f 100644
--- a/requests/structures.py
+++ b/requests/structures.py
@@ -40,7 +40,7 @@ class CaseInsensitiveDict(collections.MutableMapping):
 
     """
     def __init__(self, data=None, **kwargs):
-        self._store = dict()
+        self._store = collections.OrderedDict()
         if data is None:
             data = {}
         self.update(data, **kwargs)