diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index a93abf4..98e995b 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -22,6 +22,7 @@ class Configuration implements ConfigurationInterface
                 ->scalarNode('length')->defaultValue(5)->end()
                 ->scalarNode('width')->defaultValue(120)->end()
                 ->scalarNode('height')->defaultValue(40)->end()
+                ->scalarNode('charset')->defaultValue('abcdefhjkmnprstuvwxyz23456789')->end()
                 ->scalarNode('as_file')->defaultValue(false)->end()
                 ->scalarNode('image_folder')->defaultValue('captcha')->end()
                 ->scalarNode('web_path')->defaultValue('%kernel.root_dir%/../web')->end()
diff --git a/README.md b/README.md
index 29d9672..f687a20 100644
--- a/README.md
+++ b/README.md
@@ -100,6 +100,7 @@ You can define the following type option :
 * **width**: the width of the captcha image (default=120)
 * **height**: the height of the captcha image (default=40)
 * **length**: the length of the captcha (number of chars, default 5)
+* **charset**: the charset used for code generation (default=abcdefhjkmnprstuvwxyz23456789)
 * **as_file**: if set to true an image file will be created instead of embedding to please IE6/7 (default=false)
 * **image_folder**: name of folder for captcha images relative to public web folder in case **as_file** ist set to true (default="captcha")
 * **web_path**: absolute path to public web folder (default="%kernel.root_dir%/../web")
diff --git a/Type/CaptchaType.php b/Type/CaptchaType.php
index eb9a8f8..74269bb 100755
--- a/Type/CaptchaType.php
+++ b/Type/CaptchaType.php
@@ -45,6 +45,12 @@ class CaptchaType extends AbstractType
      */
     protected $asFile;
 
+    /**
+     * Charset used
+     * @var string
+     */
+    protected $charset;
+
     /**
      * Folder to save captcha images in,
      * relative to public web folder
@@ -78,7 +84,7 @@ class CaptchaType extends AbstractType
 
     /**
      * Session key
-     * @var String
+     * @var string
      */
     private $key = 'captcha';
 
@@ -91,6 +97,7 @@ class CaptchaType extends AbstractType
         $this->height = $config['height'];
         $this->length = $config['length'];
         $this->asFile = $config['as_file'];
+        $this->charset = $config['charset'];
         $this->imageFolder = $config['image_folder'];
         $this->webPath = $config['web_path'];
         $this->gcFreq = $config['gc_freq'];
@@ -156,8 +163,7 @@ class CaptchaType extends AbstractType
     {
         if (!$this->session->has($this->key)) {
             $value = '';
-            $charset = 'abcdefhjkmnprstuvwxyz23456789';
-            $chars = str_split($charset);
+            $chars = str_split($this->charset);
 
             for ($i=0; $i<$this->length; $i++) {
                 $value.= $chars[array_rand($chars)];