diff --git a/CHANGELOG b/CHANGELOG
index 66cf1bb3..df5c37db 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -241,6 +241,10 @@ HISTORY
 
   ++ Bug fixes:
 
+  2007-06-28 Simon Goldschmidt
+  * tcp.h, tcp.c, tcp_in.c, tcp_out.c: Added some ASSERTS and casts to prevent
+    warnings when assigning to smaller types.
+
   2007-06-28 Simon Goldschmidt
   * tcp_out.c: Added check to prevent tcp_pcb->snd_queuelen from overflowing.
 
diff --git a/src/core/tcp.c b/src/core/tcp.c
index d73cf695..7df02332 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -525,7 +525,7 @@ void
 tcp_slowtmr(void)
 {
   struct tcp_pcb *pcb, *pcb2, *prev;
-  u32_t eff_wnd;
+  u16_t eff_wnd;
   u8_t pcb_remove;      /* flag if a PCB should be removed */
   err_t err;
 
@@ -575,7 +575,7 @@ tcp_slowtmr(void)
 
         /* Reduce congestion window and ssthresh. */
         eff_wnd = LWIP_MIN(pcb->cwnd, pcb->snd_wnd);
-        pcb->ssthresh = (u16_t)(eff_wnd >> 1);
+        pcb->ssthresh = eff_wnd >> 1;
         if (pcb->ssthresh < pcb->mss) {
           pcb->ssthresh = pcb->mss * 2;
         }
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index e6fb13a8..c7aa39f2 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -676,7 +676,7 @@ tcp_receive(struct tcp_pcb *pcb)
       pcb->snd_wnd = tcphdr->wnd;
       pcb->snd_wl1 = seqno;
       pcb->snd_wl2 = ackno;
-      LWIP_DEBUGF(TCP_WND_DEBUG, ("tcp_receive: window update %"U32_F"\n", pcb->snd_wnd));
+      LWIP_DEBUGF(TCP_WND_DEBUG, ("tcp_receive: window update %"U16_F"\n", pcb->snd_wnd));
 #if TCP_WND_DEBUG
     } else {
       if (pcb->snd_wnd != tcphdr->wnd) {
@@ -745,8 +745,8 @@ tcp_receive(struct tcp_pcb *pcb)
       /* Reset the retransmission time-out. */
       pcb->rto = (pcb->sa >> 3) + pcb->sv;
 
-      /* Update the send buffer space. */
-      pcb->acked = ackno - pcb->lastack;
+      /* Update the send buffer space. Diff between the two can never exceed 64K? */
+      pcb->acked = (u16_t)(ackno - pcb->lastack);
 
       pcb->snd_buf += pcb->acked;
 
@@ -852,7 +852,9 @@ tcp_receive(struct tcp_pcb *pcb)
        incoming segment acknowledges the segment we use to take a
        round-trip time measurement. */
     if (pcb->rttest && TCP_SEQ_LT(pcb->rtseq, ackno)) {
-      m = tcp_ticks - pcb->rttest;
+      /* diff between this shouldn't exceed 32K since this are tcp timer ticks
+         and a round-trip shouldn't be that long... */
+      m = (s16_t)(tcp_ticks - pcb->rttest);
 
       LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_receive: experienced rtt %"U16_F" ticks (%"U16_F" msec).\n",
                                   m, m * TCP_SLOW_INTERVAL));
@@ -931,8 +933,10 @@ tcp_receive(struct tcp_pcb *pcb)
       off = pcb->rcv_nxt - seqno;
       p = inseg.p;
       LWIP_ASSERT("inseg.p != NULL", inseg.p);
+      LWIP_ASSERT("insane offset!", (off < 0x7fff));
       if (inseg.p->len < off) {
-        new_tot_len = inseg.p->tot_len - off;
+        LWIP_ASSERT("pbuf too short!", (((s32_t)inseg.p->tot_len) >= off));
+        new_tot_len = (u16_t)(inseg.p->tot_len - off);
         while (p->len < off) {
           off -= p->len;
           /* KJM following line changed (with addition of new_tot_len var)
@@ -942,12 +946,12 @@ tcp_receive(struct tcp_pcb *pcb)
           p->len = 0;
           p = p->next;
         }
-        if(pbuf_header(p, -off)) {
+        if(pbuf_header(p, (s16_t)-off)) {
           /* Do we need to cope with this failing?  Assert for now */
           LWIP_ASSERT("pbuf_header failed", 0);
         }
       } else {
-        if(pbuf_header(inseg.p, -off)) {
+        if(pbuf_header(inseg.p, (s16_t)-off)) {
           /* Do we need to cope with this failing?  Assert for now */
           LWIP_ASSERT("pbuf_header failed", 0);
         }
@@ -955,7 +959,7 @@ tcp_receive(struct tcp_pcb *pcb)
       /* KJM following line changed to use p->payload rather than inseg->p->payload
          to fix bug #9076 */
       inseg.dataptr = p->payload;
-      inseg.len -= pcb->rcv_nxt - seqno;
+      inseg.len -= (u16_t)(pcb->rcv_nxt - seqno);
       inseg.tcphdr->seqno = seqno = pcb->rcv_nxt;
     }
     else {
@@ -984,7 +988,7 @@ tcp_receive(struct tcp_pcb *pcb)
             TCP_SEQ_LEQ(pcb->ooseq->tcphdr->seqno, seqno + inseg.len)) {
           /* We have to trim the second edge of the incoming
              segment. */
-          inseg.len = pcb->ooseq->tcphdr->seqno - seqno;
+          inseg.len = (u16_t)(pcb->ooseq->tcphdr->seqno - seqno);
           pbuf_realloc(inseg.p, inseg.len);
         }
 #endif /* TCP_QUEUE_OOSEQ */
@@ -1126,7 +1130,7 @@ tcp_receive(struct tcp_pcb *pcb)
 
                   if (TCP_SEQ_GT(seqno + inseg.len, next->tcphdr->seqno)) {
                     /* We need to trim the incoming segment. */
-                    inseg.len = next->tcphdr->seqno - seqno;
+                    inseg.len = (u16_t)(next->tcphdr->seqno - seqno);
                     pbuf_realloc(inseg.p, inseg.len);
                   }
                   cseg = tcp_seg_copy(&inseg);
@@ -1147,7 +1151,7 @@ tcp_receive(struct tcp_pcb *pcb)
                    needed. */
                 if (TCP_SEQ_GT(seqno + inseg.len, next->tcphdr->seqno)) {
                   /* We need to trim the incoming segment. */
-                  inseg.len = next->tcphdr->seqno - seqno;
+                  inseg.len = (u16_t)(next->tcphdr->seqno - seqno);
                   pbuf_realloc(inseg.p, inseg.len);
                 }
 
@@ -1157,7 +1161,7 @@ tcp_receive(struct tcp_pcb *pcb)
                   prev->next = cseg;
                   if (TCP_SEQ_GT(prev->tcphdr->seqno + prev->len, seqno)) {
                     /* We need to trim the prev segment. */
-                    prev->len = seqno - prev->tcphdr->seqno;
+                    prev->len = (u16_t)(seqno - prev->tcphdr->seqno);
                     pbuf_realloc(prev->p, prev->len);
                   }
                 }
@@ -1172,7 +1176,7 @@ tcp_receive(struct tcp_pcb *pcb)
                 if (next->next != NULL) {
                   if (TCP_SEQ_GT(next->tcphdr->seqno + next->len, seqno)) {
                     /* We need to trim the last segment. */
-                    next->len = seqno - next->tcphdr->seqno;
+                    next->len = (u16_t)(seqno - next->tcphdr->seqno);
                     pbuf_realloc(next->p, next->len);
                   }
                 }
diff --git a/src/core/tcp_out.c b/src/core/tcp_out.c
index 8daa3d6f..0b779ceb 100644
--- a/src/core/tcp_out.c
+++ b/src/core/tcp_out.c
@@ -470,11 +470,11 @@ tcp_output(struct tcp_pcb *pcb)
 #endif /* TCP_OUTPUT_DEBUG */
 #if TCP_CWND_DEBUG
   if (seg == NULL) {
-    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"U32_F", cwnd %"U16_F", wnd %"U32_F", seg == NULL, ack %"U32_F"\n",
+    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"U16_F", cwnd %"U16_F", wnd %"U32_F", seg == NULL, ack %"U32_F"\n",
                             pcb->snd_wnd, pcb->cwnd, wnd,
                             pcb->lastack));
   } else {
-    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"U32_F", cwnd %"U16_F", wnd %"U32_F", effwnd %"U32_F", seq %"U32_F", ack %"U32_F"\n",
+    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"U16_F", cwnd %"U16_F", wnd %"U32_F", effwnd %"U32_F", seq %"U32_F", ack %"U32_F"\n",
                             pcb->snd_wnd, pcb->cwnd, wnd,
                             ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len,
                             ntohl(seg->tcphdr->seqno), pcb->lastack));
@@ -484,7 +484,7 @@ tcp_output(struct tcp_pcb *pcb)
   while (seg != NULL &&
   ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len <= wnd) {
 #if TCP_CWND_DEBUG
-    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"U32_F", cwnd %"U16_F", wnd %"U32_F", effwnd %"U32_F", seq %"U32_F", ack %"U32_F", i %"S16_F"\n",
+    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"U16_F", cwnd %"U16_F", wnd %"U32_F", effwnd %"U32_F", seq %"U32_F", ack %"U32_F", i %"S16_F"\n",
                             pcb->snd_wnd, pcb->cwnd, wnd,
                             ntohl(seg->tcphdr->seqno) + seg->len -
                             pcb->lastack,
diff --git a/src/include/lwip/tcp.h b/src/include/lwip/tcp.h
index c3724ba9..69af533d 100644
--- a/src/include/lwip/tcp.h
+++ b/src/include/lwip/tcp.h
@@ -292,10 +292,10 @@ struct tcp_pcb {
   u16_t ssthresh;
 
   /* sender variables */
-  u32_t snd_nxt,       /* next seqno to be sent */
-    snd_max,       /* Highest seqno sent. */
-    snd_wnd,       /* sender window */
-    snd_wl1, snd_wl2, /* Sequence and acknowledgement numbers of last
+  u32_t snd_nxt,   /* next seqno to be sent */
+    snd_max;       /* Highest seqno sent. */
+  u16_t snd_wnd;   /* sender window */
+  u32_t snd_wl1, snd_wl2, /* Sequence and acknowledgement numbers of last
        window update. */
     snd_lbb;       /* Sequence number of next byte to be buffered. */
 
@@ -587,6 +587,12 @@ extern struct tcp_pcb *tcp_tmp_pcb;      /* Only used for temporary storage. */
                             } while(0)
 #endif /* LWIP_DEBUG */
 
+/* finally, check some defines */
+#if TCP_WND > 0xffff
+#error TCP_WND must fit in an u16_t
+#endif
+
+
 #ifdef __cplusplus
 }
 #endif