diff --git a/Nim-for-Python-Programmers.md b/Nim-for-Python-Programmers.md
index 62187cd..adeb987 100644
--- a/Nim-for-Python-Programmers.md
+++ b/Nim-for-Python-Programmers.md
@@ -99,7 +99,7 @@ type Cat = ref object of Animal
   playfulness: float
 
 # A proc that can access and *modify* the object
-proc increase_age(self: var Cat) =
+proc increase_age(self: Cat) =
   self.age.inc()
 
 var c = Cat(name: "Tom")