diff --git a/src/Symfony/Component/Validator/Constraint.php b/src/Symfony/Component/Validator/Constraint.php
index 673b12ac00..ce7064bb40 100644
--- a/src/Symfony/Component/Validator/Constraint.php
+++ b/src/Symfony/Component/Validator/Constraint.php
@@ -214,6 +214,16 @@ abstract class Constraint
         throw new InvalidOptionsException(sprintf('The option "%s" does not exist in constraint %s', $option, get_class($this)), array($option));
     }
 
+    /**
+     * @param string $option The option name
+     *
+     * @return bool
+     */
+    public function __isset($option)
+    {
+        return 'groups' === $option;
+    }
+
     /**
      * Adds the given group if this constraint is in the Default group.
      *
diff --git a/src/Symfony/Component/Validator/Tests/Constraints/FileTest.php b/src/Symfony/Component/Validator/Tests/Constraints/FileTest.php
index 8f05b827ef..0f0e0ab6be 100644
--- a/src/Symfony/Component/Validator/Tests/Constraints/FileTest.php
+++ b/src/Symfony/Component/Validator/Tests/Constraints/FileTest.php
@@ -26,6 +26,16 @@ class FileTest extends TestCase
 
         $this->assertSame($bytes, $file->maxSize);
         $this->assertSame($binaryFormat, $file->binaryFormat);
+        $this->assertTrue($file->__isset('maxSize'));
+    }
+
+    public function testMagicIsset()
+    {
+        $file = new File(array('maxSize' => 1));
+
+        $this->assertTrue($file->__isset('maxSize'));
+        $this->assertTrue($file->__isset('groups'));
+        $this->assertFalse($file->__isset('toto'));
     }
 
     /**