diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index 515f3ba..194f7fb 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -533,7 +533,8 @@
         tdo->values[i] = PyList_GET_ITEM(values, i);
         Py_INCREF(tdo->values[i]);
     }
-    tdo->numread = len;
+    /* len <= LINKCELLS < INT_MAX */
+    tdo->numread = Py_SAFE_DOWNCAST(len, Py_ssize_t, int);
 
     if (len == LINKCELLS) {
         if (next != Py_None) {