diff --git a/tps/sem4/README.md b/tps/sem4/README.md
index 267ea6f..aa8cae1 100644
--- a/tps/sem4/README.md
+++ b/tps/sem4/README.md
@@ -291,7 +291,7 @@ Ajoutez cette méthode à vote classe Creature :
 
 ```
 before_create do
-  size = case health_points
+  self.size = case health_points
     when 0..10
       :small
     when 11..30