diff --git a/pep-0252.txt b/pep-0252.txt
index 78534aa39..aad9831b7 100644
--- a/pep-0252.txt
+++ b/pep-0252.txt
@@ -403,7 +403,7 @@ Implementation
     here, see the file Lib/test/test_descr.py.
 
     Note: the code in this branch goes beyond this PEP; it is also
-    on the way to implementing PEP 253 (Subtyping Built-in Types).
+    on the way to implementing pep-0253 (Subtyping Built-in Types).
 
 References