diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index c92499d..388ec72 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -2141,7 +2141,7 @@
 		if (it == NULL) {
 			if (PyErr_ExceptionMatches(PyExc_TypeError))
 				PyErr_Format(PyExc_TypeError,
-				    "zip argument #%d must support iteration",
+				    "zip argument #%zd must support iteration",
 				    i+1);
 			goto Fail_ret_itlist;
 		}