diff --git a/requests/sessions.py b/requests/sessions.py
index 334db58e..023edfbd 100644
--- a/requests/sessions.py
+++ b/requests/sessions.py
@@ -134,8 +134,8 @@ class SessionRedirectMixin(object):
                 url = requote_uri(url)
 
             prepared_request.url = to_native_string(url)
-            # cache the url
-            if resp.is_permanent_redirect:
+            # Cache the url, unless it redirects to itself.
+            if resp.is_permanent_redirect and req.url != prepared_request.url:
                 self.redirect_cache[req.url] = prepared_request.url
 
             # http://tools.ietf.org/html/rfc7231#section-6.4.4