diff --git a/requests/models.py b/requests/models.py
index af364102..d8456375 100644
--- a/requests/models.py
+++ b/requests/models.py
@@ -197,7 +197,7 @@ class Request(object):
                 response.status_code = getattr(resp, 'status', None)
 
                 # Make headers case-insensitive.
-                response.headers = CaseInsensitiveDict(getattr(resp, 'headers', None))
+                response.headers = CaseInsensitiveDict(getattr(resp, 'headers', {}))
 
                 # Set encoding.
                 response.encoding = get_encoding_from_headers(response.headers)