diff --git a/src/Illuminate/Validation/Rules/NotIn.php b/src/Illuminate/Validation/Rules/NotIn.php
index 7fb6574515ec..ed93bc897619 100644
--- a/src/Illuminate/Validation/Rules/NotIn.php
+++ b/src/Illuminate/Validation/Rules/NotIn.php
@@ -2,10 +2,38 @@
 
 namespace Illuminate\Validation\Rules;
 
-class NotIn extends In
+class NotIn
 {
     /**
      * The name of the rule.
      */
     protected $rule = 'not_in';
+
+    /**
+     * The accepted values.
+     *
+     * @var array
+     */
+    protected $values;
+
+    /**
+     * Create a new "not in" rule instance.
+     *
+     * @param  array  $values
+     * @return void
+     */
+    public function __construct(array $values)
+    {
+        $this->values = $values;
+    }
+
+    /**
+     * Convert the rule to a validation string.
+     *
+     * @return string
+     */
+    public function __toString()
+    {
+        return $this->rule.':'.implode(',', $this->values);
+    }
 }