diff --git a/src/udx.c b/src/udx.c
index 7e2ab71..4c9b634 100644
--- a/src/udx.c
+++ b/src/udx.c
@@ -188,6 +188,8 @@ on_bytes_acked (udx_stream_write_buf_t *wbuf, size_t bytes, bool cancelled) {
   assert(bytes <= stream->writes_queued_bytes);
   stream->writes_queued_bytes -= bytes;
 
+  if (cancelled) return;
+
   // if high watermark (262k+send window bytes queued for writing was hit)
   // stream->writes_queued_bytes > UDX_HIGH_WATERMARK + send_window_in_bytes(stream)
   // and we are now below high watermark
@@ -635,6 +637,7 @@ send_ack (udx_stream_t *stream) {
   stream->udx->packets_tx++;
   stream->udx->bytes_tx += buf.len;
 
+  // test: do we really need to defer reading EOF until after sending the ACK?
   if ((stream->status & UDX_STREAM_SHOULD_END_REMOTE) == UDX_STREAM_END_REMOTE && seq_compare(stream->remote_ended, stream->ack) <= 0) {
     stream->status |= UDX_STREAM_ENDED_REMOTE;
     if (stream->on_read != NULL) {
@@ -1298,6 +1301,10 @@ ack_packet (udx_stream_t *stream, uint32_t seq, int sack, udx_rate_sample_t *rs)
     udx_stream_write_buf_t *wbuf = wbufs[i];
 
     on_bytes_acked(wbuf, pkt_len, false);
+    if (stream->status & UDX_STREAM_DEAD) {
+      deref_packet(pkt);
+      return 2;
+    }
 
     udx_stream_write_t *write = wbuf->write;
 
@@ -1477,6 +1484,23 @@ process_packet (udx_socket_t *socket, char *buf, ssize_t buf_len, struct sockadd
   // todo: send data packet with seq=remote_acked-1
   bool is_probe = type & UDX_HEADER_HEARTBEAT;
 
+  uint32_t fack = ack;
+  for (int i = 0; i < nsack_blocks; i++) {
+    uint32_t sack_start = udx__swap_uint32_if_be(sacks[i * 2]);
+    uint32_t sack_end = udx__swap_uint32_if_be(sacks[i * 2 + 1]);
+
+    if (seq_diff(sack_start, ack) < 0) {
+      return 1;
+    }
+    if (seq_diff(sack_end, fack) > 0) {
+      fack = sack_end;
+    }
+  }
+  if (seq_diff(fack, stream->seq) > 0) {
+    return 1; // drop packet if sack.end > stream.seq
+              // ie packet purports to ack a packet we haven't sent yet
+  }
+
   if (is_probe) {
     send_ack(stream);
     return 1;
@@ -1683,6 +1707,9 @@ process_packet (udx_socket_t *socket, char *buf, ssize_t buf_len, struct sockadd
 
   if (type & UDX_HEADER_DATA_OR_END) {
     send_ack(stream);
+    if (stream->status & UDX_STREAM_DEAD) {
+      return 1;
+    }
   }
 
   if (data_inflight) {
@@ -2470,6 +2497,9 @@ udx_stream_connect (udx_stream_t *stream, udx_socket_t *socket, uint32_t remote_
   if (stream->ack_needed) {
     send_ack(stream);
     stream->ack_needed = false;
+    if (stream->status & UDX_STREAM_DEAD) {
+      return 0;
+    }
   }
 
   if (stream->keepalive_timeout_ms) {