diff --git a/README.md b/README.md
index 0fd47a2..418b628 100644
--- a/README.md
+++ b/README.md
@@ -44,8 +44,9 @@ ReverseCaptcha and PlainCaptcha must be configured separately.
 ### PlainCaptcha
 ```
 ReallySimpleCaptcha::Captcha::PlainCaptcha.configure do |config|
-  config.text_length = 6
+  config.field_name = :plain_captcha
 
+  config.text_length = 6
   # colors
   config.fill = 'darkblue'
   config.background_color = 'white'
@@ -61,7 +62,7 @@ end
 ### ReverseCaptcha
 ```
 ReallySimpleCaptcha::Captcha::ReverseCaptcha.configure do |config|
-  config.field_name = 'reverse_captcha'
+  config.field_name = :reverse_captcha
 end
 ```
 
diff --git a/lib/really_simple_captcha/captcha/plain_captcha.rb b/lib/really_simple_captcha/captcha/plain_captcha.rb
index 1b39a28..4dcae78 100644
--- a/lib/really_simple_captcha/captcha/plain_captcha.rb
+++ b/lib/really_simple_captcha/captcha/plain_captcha.rb
@@ -4,6 +4,8 @@ require 'base64'
 module ReallySimpleCaptcha::Captcha
   module PlainCaptcha
     include ActiveSupport::Configurable
+    config_accessor :field_name
+
     config_accessor :implode_amount
     config_accessor :wave_amplitude
     config_accessor :wave_length
@@ -12,6 +14,7 @@ module ReallySimpleCaptcha::Captcha
     config_accessor :background_color
     config_accessor :text_length
 
+    config.field_name = :plain_captcha
     config.text_length = 6
 
     def self.configure(&block)
@@ -20,7 +23,7 @@ module ReallySimpleCaptcha::Captcha
 
     module ViewHelpers
       def plain_captcha_tag
-        session[:plain_captcha] = ReallySimpleCaptcha::Util.random_string(PlainCaptcha.text_length)
+        session[PlainCaptcha.field_name] = ReallySimpleCaptcha::Util.random_string(PlainCaptcha.text_length)
 
         image = PlainCaptcha.generate_image(session[:plain_captcha], {
           implode_amount: PlainCaptcha.implode_amount,
@@ -33,7 +36,7 @@ module ReallySimpleCaptcha::Captcha
 
         content_tag :div, class: 'plain_captcha' do
           html = image_tag "data:image/gif;base64,#{image}", alt: "Captcha"
-          html.concat text_field_tag 'plain_captcha', nil, required: 'required', autocomplete: 'off'
+          html.concat text_field_tag PlainCaptcha.field_name, nil, required: 'required', autocomplete: 'off'
 
           html
         end
@@ -42,8 +45,8 @@ module ReallySimpleCaptcha::Captcha
 
     module ControllerHelpers
       def plain_captcha_valid?
-        res = params[:plain_captcha] == session[:plain_captcha]
-        session[:plain_captcha] = nil
+        res = params[PlainCaptcha.field_name] == session[PlainCaptcha.field_name]
+        session[PlainCaptcha.field_name] = nil
 
         res
       end