diff --git a/lib/faraday/adapter/net_http.rb b/lib/faraday/adapter/net_http.rb
index e0a037297..987977539 100644
--- a/lib/faraday/adapter/net_http.rb
+++ b/lib/faraday/adapter/net_http.rb
@@ -53,14 +53,15 @@ def build_connection(env)
       end
 
       def net_http_connection(env)
-        klass = if (proxy = env[:request][:proxy])
-                  Net::HTTP::Proxy(proxy[:uri].hostname, proxy[:uri].port,
-                                   proxy[:user], proxy[:password])
-                else
-                  Net::HTTP
-                end
+        proxy = env[:request][:proxy]
         port = env[:url].port || (env[:url].scheme == 'https' ? 443 : 80)
-        klass.new(env[:url].hostname, port)
+        if proxy
+          Net::HTTP.new(env[:url].hostname, port,
+                        proxy[:uri].hostname, proxy[:uri].port,
+                        proxy[:user], proxy[:password])
+        else
+          Net::HTTP.new(env[:url].hostname, port, nil)
+        end
       end
 
       def call(env)
@@ -182,7 +183,7 @@ def configure_request(http, req)
         end
 
         if (sec = http.respond_to?(:write_timeout=) &&
-                  request_timeout(:write, req))
+          request_timeout(:write, req))
           http.write_timeout = sec
         end
 
@@ -200,19 +201,19 @@ def ssl_cert_store(ssl)
         return ssl[:cert_store] if ssl[:cert_store]
 
         @ssl_cert_store ||= begin
-          # Use the default cert store by default, i.e. system ca certs
-          OpenSSL::X509::Store.new.tap(&:set_default_paths)
-        end
+                              # Use the default cert store by default, i.e. system ca certs
+                              OpenSSL::X509::Store.new.tap(&:set_default_paths)
+                            end
       end
 
       def ssl_verify_mode(ssl)
         ssl[:verify_mode] || begin
-          if ssl.fetch(:verify, true)
-            OpenSSL::SSL::VERIFY_PEER
-          else
-            OpenSSL::SSL::VERIFY_NONE
-          end
-        end
+                               if ssl.fetch(:verify, true)
+                                 OpenSSL::SSL::VERIFY_PEER
+                               else
+                                 OpenSSL::SSL::VERIFY_NONE
+                               end
+                             end
       end
     end
   end
diff --git a/spec/support/shared_examples/adapter.rb b/spec/support/shared_examples/adapter.rb
index 33f261182..47c0d2432 100644
--- a/spec/support/shared_examples/adapter.rb
+++ b/spec/support/shared_examples/adapter.rb
@@ -33,6 +33,7 @@
 
   let(:protocol) { ssl_mode? ? 'https' : 'http' }
   let(:remote) { "#{protocol}://example.com" }
+  let(:stub_remote) { remote }
 
   let(:conn) do
     conn_options[:ssl] ||= {}
@@ -46,7 +47,7 @@
     end
   end
 
-  let!(:request_stub) { stub_request(http_method, remote) }
+  let!(:request_stub) { stub_request(http_method, stub_remote) }
 
   after do
     expect(request_stub).to have_been_requested unless request_stub.disabled?
diff --git a/spec/support/shared_examples/request_method.rb b/spec/support/shared_examples/request_method.rb
index 05257ff6f..091c5f4ef 100644
--- a/spec/support/shared_examples/request_method.rb
+++ b/spec/support/shared_examples/request_method.rb
@@ -218,17 +218,41 @@
     end
   end
 
-  it 'handles requests with proxy' do
-    conn_options[:proxy] = 'http://google.co.uk'
+  context 'when a proxy is provided as option' do
+    before do
+      conn_options[:proxy] = 'http://google.co.uk'
+    end
+
+    it 'handles requests with proxy' do
+      res = conn.public_send(http_method, '/')
+      expect(res.status).to eq(200)
+    end
 
-    res = conn.public_send(http_method, '/')
-    expect(res.status).to eq(200)
+    it 'handles proxy failures' do
+      request_stub.to_return(status: 407)
+
+      expect { conn.public_send(http_method, '/') }.to raise_error(Faraday::ProxyAuthError)
+    end
   end
 
-  it 'handles proxy failures' do
-    conn_options[:proxy] = 'http://google.co.uk'
-    request_stub.to_return(status: 407)
+  context 'when http_proxy env variable is set' do
+    let(:proxy_url) { 'http://env-proxy.com:80' }
+
+    around do |example|
+      with_env 'http_proxy' => proxy_url do
+        example.run
+      end
+    end
+
+    it 'handles requests with proxy' do
+      res = conn.public_send(http_method, '/')
+      expect(res.status).to eq(200)
+    end
+
+    it 'handles proxy failures' do
+      request_stub.to_return(status: 407)
 
-    expect { conn.public_send(http_method, '/') }.to raise_error(Faraday::ProxyAuthError)
+      expect { conn.public_send(http_method, '/') }.to raise_error(Faraday::ProxyAuthError)
+    end
   end
 end