diff --git a/src/core/raw.c b/src/core/raw.c
index 17c664d8..96c75790 100644
--- a/src/core/raw.c
+++ b/src/core/raw.c
@@ -284,7 +284,7 @@ raw_connect(struct raw_pcb *pcb, const ip_addr_t *ipaddr)
     ip6_addr_select_zone(ip_2_ip6(&pcb->remote_ip), ip_2_ip6(&pcb->local_ip));
   }
 #endif /* LWIP_IPV6 && LWIP_IPV6_SCOPES */
-  pcb->flags |= RAW_FLAGS_CONNECTED;
+  raw_set_flags(pcb, RAW_FLAGS_CONNECTED);
   return ERR_OK;
 }
 
@@ -309,7 +309,7 @@ raw_disconnect(struct raw_pcb *pcb)
 #endif
   pcb->netif_idx = NETIF_NO_INDEX;
   /* mark PCB as unconnected */
-  pcb->flags &= ~RAW_FLAGS_CONNECTED;
+  raw_clear_flags(pcb, RAW_FLAGS_CONNECTED);
 }
 
 /**
@@ -468,7 +468,7 @@ raw_sendto_if_src(struct raw_pcb *pcb, struct pbuf *p, const ip_addr_t *dst_ip,
   } else {
     /* first pbuf q equals given pbuf */
     q = p;
-    if (pbuf_header(q, -header_size)) {
+    if (pbuf_header(q, (s16_t)-header_size)) {
       LWIP_ASSERT("Can't restore header we just removed!", 0);
       return ERR_MEM;
     }
diff --git a/src/core/tcp.c b/src/core/tcp.c
index 72ff08a1..88a2ea5b 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -71,7 +71,7 @@
    "The Dynamic and/or Private Ports are those from 49152 through 65535" */
 #define TCP_LOCAL_PORT_RANGE_START        0xc000
 #define TCP_LOCAL_PORT_RANGE_END          0xffff
-#define TCP_ENSURE_LOCAL_PORT_RANGE(port) ((u16_t)(((port) & ~TCP_LOCAL_PORT_RANGE_START) + TCP_LOCAL_PORT_RANGE_START))
+#define TCP_ENSURE_LOCAL_PORT_RANGE(port) ((u16_t)(((port) & (u16_t)~TCP_LOCAL_PORT_RANGE_START) + TCP_LOCAL_PORT_RANGE_START))
 #endif
 
 #if LWIP_TCP_KEEPALIVE
@@ -239,7 +239,7 @@ tcp_backlog_accepted(struct tcp_pcb* pcb)
     if (pcb->listener != NULL) {
       LWIP_ASSERT("accepts_pending != 0", pcb->listener->accepts_pending != 0);
       pcb->listener->accepts_pending--;
-      pcb->flags &= ~TF_BACKLOGPEND;
+      tcp_clear_flags(pcb, TF_BACKLOGPEND);
     }
   }
 }
@@ -824,13 +824,13 @@ tcp_update_rcv_ann_wnd(struct tcp_pcb *pcb)
 void
 tcp_recved(struct tcp_pcb *pcb, u16_t len)
 {
-  int wnd_inflation;
+  uint32_t wnd_inflation;
 
   /* pcb->state LISTEN not allowed here */
   LWIP_ASSERT("don't call tcp_recved for listen-pcbs",
     pcb->state != LISTEN);
 
-  pcb->rcv_wnd += len;
+  pcb->rcv_wnd = (tcpwnd_size_t)(pcb->rcv_wnd + len);
   if (pcb->rcv_wnd > TCP_WND_MAX(pcb)) {
     pcb->rcv_wnd = TCP_WND_MAX(pcb);
   } else if (pcb->rcv_wnd == 0) {
@@ -1107,7 +1107,8 @@ tcp_slowtmr_start:
            * connect to somebody (i.e., we are in SYN_SENT). */
           if (pcb->state != SYN_SENT) {
             u8_t backoff_idx = LWIP_MIN(pcb->nrtx, sizeof(tcp_backoff)-1);
-            pcb->rto = ((pcb->sa >> 3) + pcb->sv) << tcp_backoff[backoff_idx];
+            int calc_rto = ((pcb->sa >> 3) + pcb->sv) << tcp_backoff[backoff_idx];
+            pcb->rto = (s16_t)LWIP_MIN(calc_rto, 0x7FFF);
           }
 
           /* Reset the retransmission timer. */
@@ -1117,7 +1118,7 @@ tcp_slowtmr_start:
           eff_wnd = LWIP_MIN(pcb->cwnd, pcb->snd_wnd);
           pcb->ssthresh = eff_wnd >> 1;
           if (pcb->ssthresh < (tcpwnd_size_t)(pcb->mss << 1)) {
-            pcb->ssthresh = (pcb->mss << 1);
+            pcb->ssthresh = (tcpwnd_size_t)(pcb->mss << 1);
           }
           pcb->cwnd = pcb->mss;
           LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_slowtmr: cwnd %"TCPWNDSIZE_F
@@ -1174,7 +1175,7 @@ tcp_slowtmr_start:
        be retransmitted). */
 #if TCP_QUEUE_OOSEQ
     if (pcb->ooseq != NULL &&
-        (u32_t)tcp_ticks - pcb->tmr >= pcb->rto * TCP_OOSEQ_TIMEOUT) {
+        (tcp_ticks - pcb->tmr >= (u32_t)pcb->rto * TCP_OOSEQ_TIMEOUT)) {
       tcp_segs_free(pcb->ooseq);
       pcb->ooseq = NULL;
       LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_slowtmr: dropping OOSEQ queued data\n"));
@@ -1317,12 +1318,12 @@ tcp_fasttmr_start:
         LWIP_DEBUGF(TCP_DEBUG, ("tcp_fasttmr: delayed ACK\n"));
         tcp_ack_now(pcb);
         tcp_output(pcb);
-        pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
+        tcp_clear_flags(pcb, TF_ACK_DELAY | TF_ACK_NOW);
       }
       /* send pending FIN */
       if (pcb->flags & TF_CLOSEPEND) {
         LWIP_DEBUGF(TCP_DEBUG, ("tcp_fasttmr: pending FIN\n"));
-        pcb->flags &= ~(TF_CLOSEPEND);
+        tcp_clear_flags(pcb, TF_CLOSEPEND);
         tcp_close_shutdown_fin(pcb);
       }
 
@@ -1968,7 +1969,7 @@ u16_t
 tcp_eff_send_mss_netif(u16_t sendmss, struct netif *outif, const ip_addr_t *dest)
 {
   u16_t mss_s;
-  s16_t mtu;
+  u16_t mtu;
 
   LWIP_UNUSED_ARG(dest); /* in case IPv6 is disabled */
   
@@ -1994,12 +1995,13 @@ tcp_eff_send_mss_netif(u16_t sendmss, struct netif *outif, const ip_addr_t *dest
 #endif /* LWIP_IPV4 */
 
   if (mtu != 0) {
+    u16_t offset;
 #if LWIP_IPV6
 #if LWIP_IPV4
     if (IP_IS_V6(dest))
 #endif /* LWIP_IPV4 */
     {
-      mss_s = mtu - IP6_HLEN - TCP_HLEN;
+      offset = IP6_HLEN + TCP_HLEN;
     }
 #if LWIP_IPV4
     else
@@ -2007,9 +2009,10 @@ tcp_eff_send_mss_netif(u16_t sendmss, struct netif *outif, const ip_addr_t *dest
 #endif /* LWIP_IPV6 */
 #if LWIP_IPV4
     {
-      mss_s = mtu - IP_HLEN - TCP_HLEN;
+      offset = IP_HLEN + TCP_HLEN;
     }
 #endif /* LWIP_IPV4 */
+    mss_s = (mtu > offset) ? (u16_t)(mtu - offset) : 0;
     /* RFC 1122, chap 4.2.2.6:
      * Eff.snd.MSS = min(SendMSS+20, MMS_S) - TCPhdrsize - IPoptionsize
      * We correct for TCP options in tcp_write(), and don't support IP options.
diff --git a/src/include/lwip/netif.h b/src/include/lwip/netif.h
index 13af5c44..42659445 100644
--- a/src/include/lwip/netif.h
+++ b/src/include/lwip/netif.h
@@ -428,7 +428,7 @@ void netif_set_gw(struct netif *netif, const ip4_addr_t *gw);
 #endif /* LWIP_IPV4 */
 
 #define netif_set_flags(netif, set_flags)     do { (netif)->flags = (u8_t)((netif)->flags |  (set_flags)); } while(0)
-#define netif_clear_flags(netif, set_flags)   do { (netif)->flags = (u8_t)((netif)->flags & ~(set_flags)); } while(0)
+#define netif_clear_flags(netif, clr_flags)   do { (netif)->flags = (u8_t)((netif)->flags & ~(clr_flags)); } while(0)
 #define netif_is_flag_set(nefif, flag)        (((netif)->flags & (flag)) != 0)
 
 void netif_set_up(struct netif *netif);
diff --git a/src/include/lwip/prot/tcp.h b/src/include/lwip/prot/tcp.h
index 67fe7b9e..b251b80a 100644
--- a/src/include/lwip/prot/tcp.h
+++ b/src/include/lwip/prot/tcp.h
@@ -81,6 +81,7 @@ PACK_STRUCT_END
 #define TCP_FLAGS 0x3fU
 
 #define TCPH_HDRLEN(phdr) ((u16_t)(lwip_ntohs((phdr)->_hdrlen_rsvd_flags) >> 12))
+#define TCPH_HDRLEN_BYTES(phdr) ((u8_t)(TCPH_HDRLEN(phdr) << 2))
 #define TCPH_FLAGS(phdr)  ((u16_t)(lwip_ntohs((phdr)->_hdrlen_rsvd_flags) & TCP_FLAGS))
 
 #define TCPH_HDRLEN_SET(phdr, len) (phdr)->_hdrlen_rsvd_flags = lwip_htons(((len) << 12) | TCPH_FLAGS(phdr))
diff --git a/src/include/lwip/raw.h b/src/include/lwip/raw.h
index e701087b..8a872a55 100644
--- a/src/include/lwip/raw.h
+++ b/src/include/lwip/raw.h
@@ -118,6 +118,10 @@ void             raw_recv       (struct raw_pcb *pcb, raw_recv_fn recv, void *re
 #define          raw_flags(pcb) ((pcb)->flags)
 #define          raw_setflags(pcb,f)  ((pcb)->flags = (f))
 
+#define          raw_set_flags(pcb, set_flags)     do { (pcb)->flags = (u8_t)((pcb)->flags |  (set_flags)); } while(0)
+#define          raw_clear_flags(pcb, clr_flags)   do { (pcb)->flags = (u8_t)((pcb)->flags & ~(clr_flags)); } while(0)
+#define          raw_is_flag_set(pcb, flag)        (((pcb)->flags & (flag)) != 0)
+
 /* The following functions are the lower layer interface to RAW. */
 u8_t             raw_input      (struct pbuf *p, struct netif *inp);
 #define raw_init() /* Compatibility define, no init needed. */
diff --git a/src/include/lwip/tcp.h b/src/include/lwip/tcp.h
index 6bf0550b..6b7a2b1e 100644
--- a/src/include/lwip/tcp.h
+++ b/src/include/lwip/tcp.h
@@ -358,6 +358,10 @@ void             tcp_accept  (struct tcp_pcb *pcb, tcp_accept_fn accept);
 #endif /* LWIP_CALLBACK_API */
 void             tcp_poll    (struct tcp_pcb *pcb, tcp_poll_fn poll, u8_t interval);
 
+#define          tcp_set_flags(pcb, set_flags)     do { (pcb)->flags = (tcpflags_t)((pcb)->flags |  (set_flags)); } while(0)
+#define          tcp_clear_flags(pcb, clr_flags)   do { (pcb)->flags = (tcpflags_t)((pcb)->flags & ~(clr_flags)); } while(0)
+#define          tcp_is_flag_set(pcb, flag)        (((pcb)->flags & (flag)) != 0)
+
 #if LWIP_TCP_TIMESTAMPS
 #define          tcp_mss(pcb)             (((pcb)->flags & TF_TIMESTAMP) ? ((pcb)->mss - 12)  : (pcb)->mss)
 #else /* LWIP_TCP_TIMESTAMPS */
@@ -369,11 +373,11 @@ void             tcp_poll    (struct tcp_pcb *pcb, tcp_poll_fn poll, u8_t interv
 /** @ingroup tcp_raw */
 #define          tcp_sndqueuelen(pcb)     ((pcb)->snd_queuelen)
 /** @ingroup tcp_raw */
-#define          tcp_nagle_disable(pcb)   ((pcb)->flags |= TF_NODELAY)
+#define          tcp_nagle_disable(pcb)   tcp_set_flags(pcb, TF_NODELAY)
 /** @ingroup tcp_raw */
-#define          tcp_nagle_enable(pcb)    ((pcb)->flags = (tcpflags_t)((pcb)->flags & ~TF_NODELAY))
+#define          tcp_nagle_enable(pcb)    tcp_clear_flags(pcb, TF_NODELAY)
 /** @ingroup tcp_raw */
-#define          tcp_nagle_disabled(pcb)  (((pcb)->flags & TF_NODELAY) != 0)
+#define          tcp_nagle_disabled(pcb)  tcp_is_flag_set(pcb, TF_NODELAY)
 
 #if TCP_LISTEN_BACKLOG
 #define          tcp_backlog_set(pcb, new_backlog) do { \
diff --git a/src/netif/ppp/vj.c b/src/netif/ppp/vj.c
index 7899f675..3fc1a4c9 100644
--- a/src/netif/ppp/vj.c
+++ b/src/netif/ppp/vj.c
@@ -471,7 +471,7 @@ vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp)
   hlen = IPH_HL(ip) << 2;
   if (IPH_PROTO(ip) >= MAX_SLOTS
       || hlen + sizeof(struct tcp_hdr) > nb->len
-      || (hlen += TCPH_HDRLEN(((struct tcp_hdr *)&((char *)ip)[hlen])) << 2)
+      || (hlen += TCPH_HDRLEN_BYTES((struct tcp_hdr *)&((char *)ip)[hlen]))
           > nb->len
       || hlen > MAX_HDR) {
     PPPDEBUG(LOG_INFO, ("vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n",