diff --git a/src/Definition.php b/src/Definition.php
index 1b6bb08..33a57cb 100644
--- a/src/Definition.php
+++ b/src/Definition.php
@@ -17,7 +17,7 @@
  *
  * @author Graham Campbell <graham@alt-three.com>
  */
-class Definition
+final class Definition
 {
     /**
      * The model class name.