diff --git a/lib/mail_view.rb b/lib/mail_view.rb
index b9e77bf..65d9020 100644
--- a/lib/mail_view.rb
+++ b/lib/mail_view.rb
@@ -22,7 +22,7 @@ def call(env)
   end
 
   def call(env)
-    request = Rack::Request.new(env)
+    @request = Rack::Request.new(env)
 
     if request.path_info == "" || request.path_info == "/"
       links = self.actions.map do |action|
@@ -67,6 +67,10 @@ def call(env)
     def actions
       public_methods(false).map(&:to_s).sort - ['call']
     end
+    
+    def request
+      @request
+    end
 
     def email_template
       Tilt.new(email_template_path)
@@ -110,7 +114,7 @@ def find_preferred_part(mail, formats)
     end
 
     def part_body_url(part)
-      '?part=%s' % Rack::Utils.escape([part.main_type, part.sub_type].compact.join('/'))
+      "?#{request.params.merge({'part' => [part.main_type, part.sub_type].compact.join('/')}).to_param}"
     end
 
     def find_part(mail, matching_content_type)
diff --git a/lib/mail_view/email.html.erb b/lib/mail_view/email.html.erb
index 638a43f..d84c4dd 100644
--- a/lib/mail_view/email.html.erb
+++ b/lib/mail_view/email.html.erb
@@ -84,8 +84,8 @@
     <% if mail.multipart? %>
       <dd>
         <select onchange="document.getElementsByName('messageBody')[0].src=this.options[this.selectedIndex].value;">
-          <option value="?part=text%2Fhtml">View as HTML email</option>
-          <option value="?part=text%2Fplain">View as plain-text email</option>
+          <option value="?#{ request.params.merge({'part' => 'text/html' }).to_param }">View as HTML email</option>
+          <option value="?#{ request.params.merge({'part' => 'text/plain'}).to_param }">View as plain-text email</option>
         </select>
       </dd>
     <% end %>
diff --git a/test/test_mail_view.rb b/test/test_mail_view.rb
index 33c2b54..8d3d377 100644
--- a/test/test_mail_view.rb
+++ b/test/test_mail_view.rb
@@ -17,6 +17,15 @@ def plain_text_message
         yield self if block_given?
       end
     end
+    
+    def use_request_params_in_preview
+      locale = request.params['locale']
+      Mail.new do
+        to 'josh@37signals.com'
+        body "Locale: #{locale}"
+        yield self if block_given?
+      end
+    end
 
     def plain_text_message_with_display_names
       Mail.new do
@@ -145,6 +154,11 @@ def test_index
     assert_match '/html_message', last_response.body
     assert_match '/multipart_alternative', last_response.body
   end
+  
+  def test_use_request_params_in_preview
+    get '/use_request_params_in_preview?locale=en&part='
+    assert_match 'Locale: en', last_response.body
+  end
 
   def test_mounted_index
     get '/', {}, 'SCRIPT_NAME' => '/boom'