diff --git a/code-ch13/network.py b/code-ch13/network.py
index 8f3fa860..b731c2de 100644
--- a/code-ch13/network.py
+++ b/code-ch13/network.py
@@ -221,6 +221,7 @@ class PongMessage:
     def __init__(self, nonce):
         self.nonce = nonce
 
+    @classmethod
     def parse(cls, s):
         nonce = s.read(8)
         return cls(nonce)