diff --git a/requests/sessions.py b/requests/sessions.py
index ae4bcc8e79..32ca0ec1c3 100644
--- a/requests/sessions.py
+++ b/requests/sessions.py
@@ -527,18 +527,16 @@ def request(self, method, url,
         )
         prep = self.prepare_request(req)
 
-        proxies = proxies or {}
-
-        settings = self.merge_environment_settings(
-            prep.url, proxies, stream, verify, cert
-        )
-
-        # Send the request.
         send_kwargs = {
             'timeout': timeout,
             'allow_redirects': allow_redirects,
+            'verify': verify,
+            'proxies': proxies,
+            'stream': stream,
+            'cert': cert,
         }
-        send_kwargs.update(settings)
+        
+        # Send the request.
         resp = self.send(prep, **send_kwargs)
 
         return resp
@@ -628,23 +626,28 @@ def send(self, request, **kwargs):
 
         :rtype: requests.Response
         """
-        # Set defaults that the hooks can utilize to ensure they always have
-        # the correct parameters to reproduce the previous request.
-        kwargs.setdefault('stream', self.stream)
-        kwargs.setdefault('verify', self.verify)
-        kwargs.setdefault('cert', self.cert)
-        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.
         if isinstance(request, Request):
             raise ValueError('You can only send PreparedRequests.')
 
+        # Set defaults that the hooks can utilize to ensure they always have
+        # the correct parameters to reproduce the previous request.
+        stream = kwargs.get('stream')
+        verify = kwargs.get('verify')
+        cert = kwargs.get('cert')
+        proxies = kwargs.get('proxies')
+
         # Set up variables needed for resolve_redirects and dispatching of hooks
         allow_redirects = kwargs.pop('allow_redirects', True)
-        stream = kwargs.get('stream')
         hooks = request.hooks
 
+        # Merge with environment variables
+        settings = self.merge_environment_settings(
+            request.url, proxies, stream, verify, cert
+        )
+        kwargs.update(settings)
+
         # Get the appropriate adapter to use
         adapter = self.get_adapter(url=request.url)
 
@@ -704,6 +707,15 @@ def merge_environment_settings(self, url, proxies, stream, verify, cert):
 
         :rtype: dict
         """
+        
+        # Merge all the kwargs.
+        proxies = merge_setting(proxies, self.proxies)
+        stream = merge_setting(stream, self.stream)
+        verify = merge_setting(verify, self.verify)
+        cert = merge_setting(cert, self.cert)
+
+        proxies = proxies or {}
+
         # Gather clues from the surrounding environment.
         if self.trust_env:
             # Set environment's proxies.
@@ -716,13 +728,7 @@ def merge_environment_settings(self, url, proxies, stream, verify, cert):
             # with cURL.
             if verify is True or verify is None:
                 verify = (os.environ.get('REQUESTS_CA_BUNDLE') or
-                          os.environ.get('CURL_CA_BUNDLE'))
-
-        # Merge all the kwargs.
-        proxies = merge_setting(proxies, self.proxies)
-        stream = merge_setting(stream, self.stream)
-        verify = merge_setting(verify, self.verify)
-        cert = merge_setting(cert, self.cert)
+                    os.environ.get('CURL_CA_BUNDLE') or verify)
 
         return {'verify': verify, 'proxies': proxies, 'stream': stream,
                 'cert': cert}
diff --git a/tests/test_requests.py b/tests/test_requests.py
index 223c36e363..1d68432c1f 100644
--- a/tests/test_requests.py
+++ b/tests/test_requests.py
@@ -590,6 +590,33 @@ def test_respect_proxy_env_on_request(self, httpbin):
                 session = requests.Session()
                 session.request(method='GET', url=httpbin())
 
+    def test_merge_environment_settings_precedence(self):
+        session = requests.Session()
+        merge_settings_args = {
+            'url':'http://localhost:1',
+            'proxies':{
+                'http': 'http://argument'
+            },
+            'stream':None,
+            'verify':None,
+            'cert':None,
+        }
+        with override_environ(http_proxy='http://environment'):
+            session.proxies.update(http='http://attribute')
+            settings = session.merge_environment_settings(**merge_settings_args)
+            assert settings['proxies']['http'] == 'http://argument'
+
+            merge_settings_args['proxies'] = None
+            settings = session.merge_environment_settings(**merge_settings_args)
+            assert settings['proxies']['http'] == 'http://attribute'
+
+            session.proxies = None
+            settings = session.merge_environment_settings(**merge_settings_args)
+            assert settings['proxies']['http'] == 'http://environment'
+
+        settings = session.merge_environment_settings(**merge_settings_args)
+        assert settings['proxies'] == {}
+
     def test_basicauth_with_netrc(self, httpbin):
         auth = ('user', 'pass')
         wrong_auth = ('wronguser', 'wrongpass')