diff --git a/README.md b/README.md
index 9c2073f..1b0ca27 100644
--- a/README.md
+++ b/README.md
@@ -93,6 +93,21 @@ if($v->validate()) {
  * `dateBefore` - Field is a valid date and is before the given date
  * `dateAfter` - Field is a valid date and is after the given date
 
+## Adding Custom Validation Rules
+
+To add your own validation rule, use the `addRule` method with a rule
+name, a custom callback or closure, and a error message to display in
+case of an error. The callback provided should return boolean true or
+false.
+
+```
+Valitron\Validation::addRule('alwaysFail', function($field, $value,
+array $params) {
+    return false;
+}, 'Everything you do is wrong. You fail.');
+```
+
+
 ## Contributing
 
 1. Fork it
diff --git a/composer.json b/composer.json
index eaa4c6e..7990087 100644
--- a/composer.json
+++ b/composer.json
@@ -1,6 +1,6 @@
 {
     "name": "vlucas/valitron",
-    "version": "1.0.0",
+    "version": "1.0.1",
     "type": "library",
     "description": "Simple, elegant, stand-alone validation library with NO dependencies",
     "keywords": ["validation", "validator", "valid"],
diff --git a/src/Valitron/Validator.php b/src/Valitron/Validator.php
index 2e44327..3282e4f 100644
--- a/src/Valitron/Validator.php
+++ b/src/Valitron/Validator.php
@@ -21,6 +21,8 @@ class Validator
     protected static $_rules = array();
     protected static $_ruleMessages = array();
 
+    const ERROR_DEFAULT = 'Invalid';
+
 
     /**
      *  Setup validation
@@ -470,13 +472,14 @@ class Validator
     /**
      * Register new validation rule callback
      */
-    public static function addRule($name, $callback)
+    public static function addRule($name, $callback, $message = self::ERROR_DEFAULT)
     {
         if(!is_callable($callback)) {
             throw new \InvalidArgumentException("Second argument must be a valid callback. Given argument was not callable.");
         }
 
         static::$_rules[$name] = $callback;
+        static::$_ruleMessages[$name] = $message;
     }
 
     /**
@@ -492,7 +495,7 @@ class Validator
         }
 
         // Ensure rule has an accompanying message
-        $message = isset(static::$_ruleMessages[$rule]) ? static::$_ruleMessages[$rule] : 'Invalid';
+        $message = isset(static::$_ruleMessages[$rule]) ? static::$_ruleMessages[$rule] : self::ERROR_DEFAULT;
 
         // Get any other arguments passed to function
         $params = array_slice(func_get_args(), 2);