diff --git a/src/core/dns.c b/src/core/dns.c
index 69c1e663..ed0264d4 100644
--- a/src/core/dns.c
+++ b/src/core/dns.c
@@ -694,8 +694,8 @@ dns_send(struct dns_table_entry* entry)
   LWIP_ASSERT("dns server has no IP address set", !ip_addr_isany(&dns_servers[entry->server_idx]));
 
   /* if here, we have either a new query or a retry on a previous query to process */
-  p = pbuf_alloc(PBUF_TRANSPORT, SIZEOF_DNS_HDR + strlen(entry->name) + 2 +
-                 SIZEOF_DNS_QUERY, PBUF_RAM);
+  p = pbuf_alloc(PBUF_TRANSPORT, (u16_t)(SIZEOF_DNS_HDR + strlen(entry->name) + 2 +
+                 SIZEOF_DNS_QUERY), PBUF_RAM);
   if (p != NULL) {
     /* fill dns header */
     memset(&hdr, 0, SIZEOF_DNS_HDR);
@@ -714,7 +714,7 @@ dns_send(struct dns_table_entry* entry)
       for(n = 0; *hostname != '.' && *hostname != 0; ++hostname) {
         ++n;
       }
-      copy_len = hostname - hostname_part;
+      copy_len = (u16_t)(hostname - hostname_part);
       pbuf_put_at(p, query_idx, n);
       pbuf_take_at(p, hostname_part, copy_len, query_idx + 1);
       query_idx += n + 1;
@@ -759,7 +759,7 @@ dns_alloc_random_port(void)
     return NULL;
   }
   do {
-    u16_t port = DNS_RAND_TXID();
+    u16_t port = (u16_t)DNS_RAND_TXID();
     if (!DNS_PORT_ALLOWED(port)) {
       /* this port is not allowed, try again */
       err = ERR_USE;
@@ -875,7 +875,7 @@ dns_create_txid(void)
   u8_t i;
 
 again:
-  txid = DNS_RAND_TXID();
+  txid = (u16_t)DNS_RAND_TXID();
 
   /* check whether the ID is unique */
   for (i = 0; i < DNS_TABLE_SIZE; i++) {
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index c82aed9f..6e913e30 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -1596,7 +1596,7 @@ tcp_receive(struct tcp_pcb *pcb)
                       TCPH_FLAGS_SET(next->next->tcphdr, TCPH_FLAGS(next->next->tcphdr) &~ TCP_FIN);
                     }
                     /* Adjust length of segment to fit in the window. */
-                    next->next->len = pcb->rcv_nxt + pcb->rcv_wnd - seqno;
+                    next->next->len = (u16_t)(pcb->rcv_nxt + pcb->rcv_wnd - seqno);
                     pbuf_realloc(next->next->p, next->next->len);
                     tcplen = TCP_TCPLEN(next->next);
                     LWIP_ASSERT("tcp_receive: segment not trimmed correctly to rcv_wnd\n",
@@ -1657,7 +1657,7 @@ static u8_t tcp_getoptbyte(void)
     u8_t* opts = (u8_t *)tcphdr + TCP_HLEN;
     return opts[tcp_optidx++];
   } else {
-    u8_t idx = tcp_optidx++ - tcphdr_opt1len;
+    u8_t idx = (u8_t)(tcp_optidx++ - tcphdr_opt1len);
     return tcphdr_opt2[idx];
   }
 }
diff --git a/src/include/lwip/ip4.h b/src/include/lwip/ip4.h
index 1375654f..db1866dc 100644
--- a/src/include/lwip/ip4.h
+++ b/src/include/lwip/ip4.h
@@ -97,7 +97,7 @@ PACK_STRUCT_END
 #define IPH_PROTO(hdr) ((hdr)->_proto)
 #define IPH_CHKSUM(hdr) ((hdr)->_chksum)
 
-#define IPH_VHL_SET(hdr, v, hl) (hdr)->_v_hl = (((v) << 4) | (hl))
+#define IPH_VHL_SET(hdr, v, hl) (hdr)->_v_hl = (u8_t)((((v) << 4) | (hl)))
 #define IPH_TOS_SET(hdr, tos) (hdr)->_tos = (tos)
 #define IPH_LEN_SET(hdr, len) (hdr)->_len = (len)
 #define IPH_ID_SET(hdr, id) (hdr)->_id = (id)