diff --git a/Modules/mpzmodule.c b/Modules/mpzmodule.c
index 1aaf787e6b5..af44abf3c69 100644
--- a/Modules/mpzmodule.c
+++ b/Modules/mpzmodule.c
@@ -143,7 +143,7 @@ mpz_format(objp, base, withname)
 {
 	mpzobject *mpzp = (mpzobject *)objp;
 	PyStringObject *strobjp;
-	int i;
+	size_t i;
 	int cmpres;
 	int taglong;
 	char *cp;