fix2

diff --git a/src/plumbing/tsfix.c b/src/plumbing/tsfix.c
index c75df63..afb65e3 100644
--- a/src/plumbing/tsfix.c
+++ b/src/plumbing/tsfix.c
@@ -235,7 +235,7 @@ normalize_ts(tsfix_t *tf, tfstream_t *tfs, th_pkt_t *pkt, int backlog)
   pkt->pkt_dts &= PTS_MASK;

   /* Subtract the transport wide start offset */
-  dts = pkt->pkt_dts - ref;
+  dts = (pkt->pkt_dts - ref) & PTS_MASK;

   if (tfs->tfs_last_dts_norm == PTS_UNSET) {
     if (dts < 0 || pkt->pkt_err) {