diff --git a/Modules/zlibmodule.c b/Modules/zlibmodule.c
index 52744b967eb..0d2e188b433 100644
--- a/Modules/zlibmodule.c
+++ b/Modules/zlibmodule.c
@@ -3,6 +3,7 @@
 
 /* Windows users:  read Python's PCbuild\readme.txt */
 
+#define PY_SSIZE_T_CLEAN
 
 #include "Python.h"
 #include "structmember.h"