diff --git a/pack-write.c b/pack-write.c
index de72f44dc8ea50..ae2e481e5554cf 100644
--- a/pack-write.c
+++ b/pack-write.c
@@ -25,7 +25,7 @@ void fixup_pack_header_footer(int pack_fd,
 
 	buf = xmalloc(buf_sz);
 	for (;;) {
-		size_t n = xread(pack_fd, buf, buf_sz);
+		ssize_t n = xread(pack_fd, buf, buf_sz);
 		if (!n)
 			break;
 		if (n < 0)