diff --git a/omega-target-chromium-extension/src/module/proxy/proxy_impl_listener.coffee b/omega-target-chromium-extension/src/module/proxy/proxy_impl_listener.coffee
index eb60866a..cfccc4e6 100644
--- a/omega-target-chromium-extension/src/module/proxy/proxy_impl_listener.coffee
+++ b/omega-target-chromium-extension/src/module/proxy/proxy_impl_listener.coffee
@@ -1,11 +1,11 @@
 OmegaTarget = require('omega-target')
 # The browser only accepts native promises as onRequest return values.
 # DO NOT USE Bluebird Promises here!
-NativePromise = Promise
+NativePromise = Promise ? null
 ProxyImpl = require('./proxy_impl')
 
 class ListenerProxyImpl extends ProxyImpl
-  @isSupported: -> browser?.proxy?.onRequest?
+  @isSupported: -> Promise? and browser?.proxy?.onRequest?
   features: ['fullUrl', 'socks5Auth']
   constructor: ->
     super(arguments...)
diff --git a/omega-web/src/coffee/log_error.coffee b/omega-web/src/coffee/log_error.coffee
index 056f11cb..a58bd9f4 100644
--- a/omega-web/src/coffee/log_error.coffee
+++ b/omega-web/src/coffee/log_error.coffee
@@ -1,6 +1,6 @@
 window.onerror = (message, url, line, col, err) ->
   log = localStorage['log'] || ''
-  if err.stack
+  if err?.stack
     log += err.stack + '\n\n'
   else
     log += "#{url}:#{line}:#{col}:\t#{message}\n\n"