1 files changed, 1 insertions, 0 deletions
diff --git a/sprintf.c b/sprintf.c
index 254b080d9..129c4b78a 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -868,6 +868,7 @@ ruby__sfvwrite(fp, uio)
     if ((len = uio->uio_resid) == 0)
 	return 0;
     CHECK(len);
+    buf += blen;
     fp->_w = bsiz;
     for (iov = uio->uio_iov; len > 0; ++iov) {
 	MEMCPY(buf, iov->iov_base, char, n = iov->iov_len);