diff --git a/CHANGELOG b/CHANGELOG
index 84021054..11b9a93f 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -526,6 +526,10 @@ HISTORY
 
   ++ Bug fixes:
 
+  2007-12-20 Kieran Mansley (based on patch from Per-Henrik Lundbolm)
+  * tcp.c, tcp_in.c, tcp_out.c, tcp.h: fix bug #20199 (better handling
+    of silly window avoidance and prevent lwIP from shrinking the window)
+
   2007-12-04 Simon Goldschmidt
   * tcp.c, tcp_in.c: fix bug #21699 (segment leak in ooseq processing when last
     data packet was lost): add assert that all segment lists are empty in
diff --git a/src/core/tcp.c b/src/core/tcp.c
index 40256d2e..93c4252e 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -385,9 +385,14 @@ tcp_recved(struct tcp_pcb *pcb, u16_t len)
 {
   if ((u32_t)pcb->rcv_wnd + len > TCP_WND) {
     pcb->rcv_wnd = TCP_WND;
+    pcb->rcv_ann_wnd = TCP_WND;
   } else {
     pcb->rcv_wnd += len;
+    if (pcb->rcv_wnd >= pcb->mss) {
+      pcb->rcv_ann_wnd = pcb->rcv_wnd;
+    }
   }
+
   if (!(pcb->flags & TF_ACK_DELAY) &&
      !(pcb->flags & TF_ACK_NOW)) {
     /*
@@ -494,6 +499,7 @@ tcp_connect(struct tcp_pcb *pcb, struct ip_addr *ipaddr, u16_t port,
   pcb->lastack = iss - 1;
   pcb->snd_lbb = iss - 1;
   pcb->rcv_wnd = TCP_WND;
+  pcb->rcv_ann_wnd = TCP_WND;
   pcb->snd_wnd = TCP_WND;
   /* The send MSS is updated when an MSS option is received. */
   pcb->mss = (TCP_MSS > 536) ? 536 : TCP_MSS;
@@ -936,6 +942,7 @@ tcp_alloc(u8_t prio)
     pcb->snd_buf = TCP_SND_BUF;
     pcb->snd_queuelen = 0;
     pcb->rcv_wnd = TCP_WND;
+    pcb->rcv_ann_wnd = TCP_WND;
     pcb->tos = 0;
     pcb->ttl = TCP_TTL;
     /* The send MSS is updated when an MSS option is received. */
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index 8c16bfb3..beffcff4 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -477,10 +477,8 @@ tcp_process(struct tcp_pcb *pcb)
         acceptable = 1;
       }
     } else {
-      /*if (TCP_SEQ_GEQ(seqno, pcb->rcv_nxt) &&
-          TCP_SEQ_LEQ(seqno, pcb->rcv_nxt + pcb->rcv_wnd)) {
-      */
-      if (TCP_SEQ_BETWEEN(seqno, pcb->rcv_nxt, pcb->rcv_nxt+pcb->rcv_wnd)) {
+      if (TCP_SEQ_BETWEEN(seqno, pcb->rcv_nxt, 
+                          pcb->rcv_nxt+pcb->rcv_ann_wnd)) {
         acceptable = 1;
       }
     }
@@ -549,7 +547,7 @@ tcp_process(struct tcp_pcb *pcb)
       /* Call the user specified function to call when sucessfully
        * connected. */
       TCP_EVENT_CONNECTED(pcb, ERR_OK, err);
-      tcp_ack(pcb);
+      tcp_ack_now(pcb);
     }
     /* received ACK? possibly a half-open connection */
     else if (flags & TCP_ACK) {
@@ -1001,9 +999,8 @@ tcp_receive(struct tcp_pcb *pcb)
     /* The sequence number must be within the window (above rcv_nxt
        and below rcv_nxt + rcv_wnd) in order to be further
        processed. */
-    /*if (TCP_SEQ_GEQ(seqno, pcb->rcv_nxt) &&
-      TCP_SEQ_LT(seqno, pcb->rcv_nxt + pcb->rcv_wnd)) {*/
-    if (TCP_SEQ_BETWEEN(seqno, pcb->rcv_nxt, pcb->rcv_nxt + pcb->rcv_wnd - 1)){
+    if (TCP_SEQ_BETWEEN(seqno, pcb->rcv_nxt, 
+                        pcb->rcv_nxt + pcb->rcv_ann_wnd - 1)){
       if (pcb->rcv_nxt == seqno) {
         accepted_inseq = 1; 
         /* The incoming segment is the next in sequence. We check if
@@ -1045,6 +1042,12 @@ tcp_receive(struct tcp_pcb *pcb)
           pcb->rcv_wnd -= tcplen;
         }
 
+        if (pcb->rcv_ann_wnd < tcplen) {
+          pcb->rcv_ann_wnd = 0;
+        } else {
+          pcb->rcv_ann_wnd -= tcplen;
+        }
+
         /* If there is data in the segment, we make preparations to
            pass this up to the application. The ->recv_data variable
            is used for holding the pbuf that goes to the
@@ -1081,6 +1084,12 @@ tcp_receive(struct tcp_pcb *pcb)
           } else {
             pcb->rcv_wnd -= TCP_TCPLEN(cseg);
           }
+          if (pcb->rcv_ann_wnd < TCP_TCPLEN(cseg)) {
+            pcb->rcv_ann_wnd = 0;
+          } else {
+            pcb->rcv_ann_wnd -= TCP_TCPLEN(cseg);
+          }
+
           if (cseg->p->tot_len > 0) {
             /* Chain this pbuf onto the pbuf that we will pass to
                the application. */
@@ -1235,9 +1244,8 @@ tcp_receive(struct tcp_pcb *pcb)
 
       }
     } else {
-      /*if (TCP_SEQ_GT(pcb->rcv_nxt, seqno) ||
-        TCP_SEQ_GEQ(seqno, pcb->rcv_nxt + pcb->rcv_wnd)) {*/
-      if(!TCP_SEQ_BETWEEN(seqno, pcb->rcv_nxt, pcb->rcv_nxt + pcb->rcv_wnd-1)){
+      if(!TCP_SEQ_BETWEEN(seqno, pcb->rcv_nxt, 
+                          pcb->rcv_nxt + pcb->rcv_ann_wnd-1)){
         tcp_ack_now(pcb);
       }
     }
diff --git a/src/core/tcp_out.c b/src/core/tcp_out.c
index 0b1c0cbf..8457af90 100644
--- a/src/core/tcp_out.c
+++ b/src/core/tcp_out.c
@@ -460,7 +460,7 @@ tcp_output(struct tcp_pcb *pcb)
     tcphdr->seqno = htonl(pcb->snd_nxt);
     tcphdr->ackno = htonl(pcb->rcv_nxt);
     TCPH_FLAGS_SET(tcphdr, TCP_ACK);
-    tcphdr->wnd = htons(pcb->rcv_wnd);
+    tcphdr->wnd = htons(pcb->rcv_ann_wnd);
     tcphdr->urgp = 0;
     TCPH_HDRLEN_SET(tcphdr, 5);
 
@@ -593,13 +593,8 @@ tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb)
    wnd fields remain. */
   seg->tcphdr->ackno = htonl(pcb->rcv_nxt);
 
-  /* silly window avoidance */
-  if (pcb->rcv_wnd < pcb->mss) {
-    seg->tcphdr->wnd = 0;
-  } else {
-    /* advertise our receive window size in this TCP segment */
-    seg->tcphdr->wnd = htons(pcb->rcv_wnd);
-  }
+  /* advertise our receive window size in this TCP segment */
+  seg->tcphdr->wnd = htons(pcb->rcv_ann_wnd);
 
   /* If we don't have a local IP address, we get one by
      calling ip_route(). */
@@ -815,15 +810,15 @@ tcp_keepalive(struct tcp_pcb *pcb)
   LWIP_ASSERT("check that first pbuf can hold struct tcp_hdr",
               (p->len >= sizeof(struct tcp_hdr)));
 
-   tcphdr = p->payload;
-   tcphdr->src = htons(pcb->local_port);
-   tcphdr->dest = htons(pcb->remote_port);
-   tcphdr->seqno = htonl(pcb->snd_nxt - 1);
-   tcphdr->ackno = htonl(pcb->rcv_nxt);
-   TCPH_FLAGS_SET(tcphdr, 0);
-   tcphdr->wnd = htons(pcb->rcv_wnd);
-   tcphdr->urgp = 0;
-   TCPH_HDRLEN_SET(tcphdr, 5);
+  tcphdr = p->payload;
+  tcphdr->src = htons(pcb->local_port);
+  tcphdr->dest = htons(pcb->remote_port);
+  tcphdr->seqno = htonl(pcb->snd_nxt - 1);
+  tcphdr->ackno = htonl(pcb->rcv_nxt);
+  TCPH_FLAGS_SET(tcphdr, 0);
+  tcphdr->wnd = htons(pcb->rcv_ann_wnd);
+  tcphdr->urgp = 0;
+  TCPH_HDRLEN_SET(tcphdr, 5);
 
    tcphdr->chksum = 0;
 #if CHECKSUM_GEN_TCP
diff --git a/src/include/lwip/tcp.h b/src/include/lwip/tcp.h
index 6130d196..ebe7ed3d 100644
--- a/src/include/lwip/tcp.h
+++ b/src/include/lwip/tcp.h
@@ -281,7 +281,8 @@ struct tcp_pcb {
   /* receiver variables */
   u32_t rcv_nxt;   /* next seqno expected */
   u16_t rcv_wnd;   /* receiver window */
-  
+  u16_t rcv_ann_wnd; /* announced receive window */
+
   /* Timers */
   u32_t tmr;
   u8_t polltmr, pollinterval;