diff --git a/atom/browser/api/atom_api_web_contents.cc b/atom/browser/api/atom_api_web_contents.cc
index 8db86f35934a..c84ace171af6 100644
--- a/atom/browser/api/atom_api_web_contents.cc
+++ b/atom/browser/api/atom_api_web_contents.cc
@@ -6,12 +6,15 @@
 
 #include <set>
 
+#include "atom/browser/browser.h"
 #include "atom/browser/api/atom_api_session.h"
 #include "atom/browser/atom_browser_client.h"
 #include "atom/browser/atom_browser_context.h"
 #include "atom/browser/atom_browser_main_parts.h"
 #include "atom/browser/native_window.h"
 #include "atom/browser/web_view_guest_delegate.h"
+#include "atom/common/atom_version.h"
+#include "atom/common/chrome_version.h"
 #include "atom/common/api/api_messages.h"
 #include "atom/common/event_emitter_caller.h"
 #include "atom/common/native_mate_converters/gfx_converter.h"
@@ -20,6 +23,7 @@
 #include "atom/common/native_mate_converters/string16_converter.h"
 #include "atom/common/native_mate_converters/value_converter.h"
 #include "base/strings/string_util.h"
+#include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "brightray/browser/inspectable_web_contents.h"
 #include "chrome/browser/printing/print_view_manager_basic.h"
@@ -36,10 +40,12 @@
 #include "content/public/browser/storage_partition.h"
 #include "content/public/browser/site_instance.h"
 #include "content/public/browser/web_contents.h"
+#include "content/public/common/user_agent.h"
 #include "native_mate/callback.h"
 #include "native_mate/dictionary.h"
 #include "native_mate/object_template_builder.h"
 #include "net/http/http_response_headers.h"
+#include "net/url_request/static_http_user_agent_settings.h"
 #include "net/url_request/url_request_context.h"
 
 #include "atom/common/node_includes.h"
@@ -51,6 +57,20 @@ struct PrintSettings {
   bool print_background;
 };
 
+std::string RemoveWhitespace(const std::string& str) {
+  std::string trimmed;
+  if (base::RemoveChars(str, " ", &trimmed))
+    return trimmed;
+  else
+    return str;
+}
+
+void SetUserAgentInIO(scoped_refptr<net::URLRequestContextGetter> getter,
+                      std::string user_agent) {
+  getter->GetURLRequestContext()->set_http_user_agent_settings(
+      new net::StaticHttpUserAgentSettings("en-us,en", user_agent));
+}
+
 }  // namespace
 
 namespace mate {
@@ -167,6 +187,7 @@ WebContents::WebContents(const mate::Dictionary& options) {
   Observe(web_contents);
   AttachAsUserData(web_contents);
   InitWithWebContents(web_contents);
+  SetUserAgent(std::string());
 
   if (is_guest) {
     guest_delegate_->Initialize(this);
@@ -546,7 +567,22 @@ bool WebContents::IsCrashed() const {
 }
 
 void WebContents::SetUserAgent(const std::string& user_agent) {
+  if (user_agent.empty()) {
+    // Default User Agent.
+    Browser* browser = Browser::Get();
+    std::string product_name = base::StringPrintf(
+        "%s/%s Chrome/%s " ATOM_PRODUCT_NAME "/" ATOM_VERSION_STRING,
+        RemoveWhitespace(browser->GetName()).c_str(),
+        browser->GetVersion().c_str(),
+        CHROME_VERSION_STRING);
+    const_cast<std::string&>(user_agent) =
+        content::BuildUserAgentFromProduct(product_name);
+  }
   web_contents()->SetUserAgentOverride(user_agent);
+  scoped_refptr<net::URLRequestContextGetter> getter =
+      web_contents()->GetBrowserContext()->GetRequestContext();
+  getter->GetNetworkTaskRunner()->PostTask(FROM_HERE,
+      base::Bind(&SetUserAgentInIO, getter, user_agent));
 }
 
 void WebContents::InsertCSS(const std::string& css) {
diff --git a/atom/browser/native_window.cc b/atom/browser/native_window.cc
index c9f209a3a2b4..b9e765315b6a 100644
--- a/atom/browser/native_window.cc
+++ b/atom/browser/native_window.cc
@@ -10,11 +10,8 @@
 
 #include "atom/browser/atom_browser_context.h"
 #include "atom/browser/atom_browser_main_parts.h"
-#include "atom/browser/browser.h"
 #include "atom/browser/window_list.h"
 #include "atom/common/api/api_messages.h"
-#include "atom/common/atom_version.h"
-#include "atom/common/chrome_version.h"
 #include "atom/common/native_mate_converters/image_converter.h"
 #include "atom/common/native_mate_converters/file_path_converter.h"
 #include "atom/common/options_switches.h"
@@ -24,7 +21,6 @@
 #include "base/prefs/pref_service.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/string_number_conversions.h"
-#include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "brightray/browser/inspectable_web_contents.h"
 #include "brightray/browser/inspectable_web_contents_view.h"
@@ -36,7 +32,6 @@
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/renderer_preferences.h"
-#include "content/public/common/user_agent.h"
 #include "content/public/common/web_preferences.h"
 #include "ipc/ipc_message_macros.h"
 #include "native_mate/dictionary.h"
@@ -73,14 +68,6 @@ const char* kWebRuntimeFeatures[] = {
   switches::kPageVisibility,
 };
 
-std::string RemoveWhitespace(const std::string& str) {
-  std::string trimmed;
-  if (base::RemoveChars(str, " ", &trimmed))
-    return trimmed;
-  else
-    return str;
-}
-
 }  // namespace
 
 NativeWindow::NativeWindow(
@@ -130,16 +117,6 @@ NativeWindow::NativeWindow(
   options.Get(switches::kZoomFactor, &zoom_factor_);
 
   WindowList::AddWindow(this);
-
-  // Override the user agent to contain application and atom-shell's version.
-  Browser* browser = Browser::Get();
-  std::string product_name = base::StringPrintf(
-      "%s/%s Chrome/%s " ATOM_PRODUCT_NAME "/" ATOM_VERSION_STRING,
-      RemoveWhitespace(browser->GetName()).c_str(),
-      browser->GetVersion().c_str(),
-      CHROME_VERSION_STRING);
-  web_contents()->GetMutableRendererPrefs()->user_agent_override =
-      content::BuildUserAgentFromProduct(product_name);
 }
 
 NativeWindow::~NativeWindow() {