diff --git a/requests/sessions.py b/requests/sessions.py
index fdf7e9fe35..39281eb1f1 100644
--- a/requests/sessions.py
+++ b/requests/sessions.py
@@ -633,7 +633,7 @@ def send(self, request, **kwargs):
         kwargs.setdefault('stream', self.stream)
         kwargs.setdefault('verify', self.verify)
         kwargs.setdefault('cert', self.cert)
-        kwargs.setdefault('proxies', 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.
diff --git a/tests/test_requests.py b/tests/test_requests.py
index 5b6a7f5847..223c36e363 100644
--- a/tests/test_requests.py
+++ b/tests/test_requests.py
@@ -40,6 +40,9 @@
 # listening on that port)
 TARPIT = 'http://10.255.255.1'
 
+# This is to avoid waiting the timeout of using TARPIT
+INVALID_PROXY='http://localhost:1'
+
 try:
     from ssl import SSLContext
     del SSLContext
@@ -551,6 +554,42 @@ def test_proxy_error_on_bad_url(self, httpbin, httpbin_secure):
         with pytest.raises(InvalidProxyURL):
             requests.get(httpbin(), proxies={'http': 'http:///example.com:8080'})
 
+    def test_respect_proxy_env_on_send_self_prepared_request(self, httpbin):
+        with override_environ(http_proxy=INVALID_PROXY):
+            with pytest.raises(ProxyError):
+                session = requests.Session()
+                request = requests.Request('GET', httpbin())
+                session.send(request.prepare())
+
+    def test_respect_proxy_env_on_send_session_prepared_request(self, httpbin):
+        with override_environ(http_proxy=INVALID_PROXY):
+            with pytest.raises(ProxyError):
+                session = requests.Session()
+                request = requests.Request('GET', httpbin())
+                prepared = session.prepare_request(request)
+                session.send(prepared)
+
+    def test_respect_proxy_env_on_send_with_redirects(self, httpbin):
+        with override_environ(http_proxy=INVALID_PROXY):
+            with pytest.raises(ProxyError):
+                session = requests.Session()
+                url = httpbin('redirect/1')
+                print(url)
+                request = requests.Request('GET', url)
+                session.send(request.prepare())
+
+    def test_respect_proxy_env_on_get(self, httpbin):
+        with override_environ(http_proxy=INVALID_PROXY):
+            with pytest.raises(ProxyError):
+                session = requests.Session()
+                session.get(httpbin())
+
+    def test_respect_proxy_env_on_request(self, httpbin):
+        with override_environ(http_proxy=INVALID_PROXY):
+            with pytest.raises(ProxyError):
+                session = requests.Session()
+                session.request(method='GET', url=httpbin())
+
     def test_basicauth_with_netrc(self, httpbin):
         auth = ('user', 'pass')
         wrong_auth = ('wronguser', 'wrongpass')