diff --git a/requests/sessions.py b/requests/sessions.py
index 19b18de050..ae4bcc8e79 100644
--- a/requests/sessions.py
+++ b/requests/sessions.py
@@ -633,8 +633,7 @@ def send(self, request, **kwargs):
         kwargs.setdefault('stream', self.stream)
         kwargs.setdefault('verify', self.verify)
         kwargs.setdefault('cert', self.cert)
-        if 'proxies' not in kwargs:
-            kwargs['proxies'] = self.rebuild_proxies(request, self.proxies)
+        kwargs.setdefault('proxies', self.rebuild_proxies(request, self.proxies))
 
         # It's possible that users might accidentally send a Request object.
         # Guard against that specific failure case.