diff --git a/mongoose.c b/mongoose.c
index 2f0db086..83bea6b0 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -4407,12 +4407,13 @@ static struct ip *tx_ip(struct mg_tcpip_if *ifp, uint8_t *mac_dst,
   return ip;
 }
 
-static void tx_udp(struct mg_tcpip_if *ifp, uint8_t *mac_dst, uint32_t ip_src,
+static bool tx_udp(struct mg_tcpip_if *ifp, uint8_t *mac_dst, uint32_t ip_src,
                    uint16_t sport, uint32_t ip_dst, uint16_t dport,
                    const void *buf, size_t len) {
   struct ip *ip =
       tx_ip(ifp, mac_dst, 17, ip_src, ip_dst, len + sizeof(struct udp));
   struct udp *udp = (struct udp *) (ip + 1);
+  size_t eth_len;
   // MG_DEBUG(("UDP XX LEN %d %d", (int) len, (int) ifp->tx.len));
   udp->sport = sport;
   udp->dport = dport;
@@ -4426,7 +4427,8 @@ static void tx_udp(struct mg_tcpip_if *ifp, uint8_t *mac_dst, uint32_t ip_src,
   udp->csum = csumfin(cs);
   memmove(udp + 1, buf, len);
   // MG_DEBUG(("UDP LEN %d %d", (int) len, (int) ifp->frame_len));
-  ether_output(ifp, sizeof(struct eth) + sizeof(*ip) + sizeof(*udp) + len);
+  eth_len = sizeof(struct eth) + sizeof(*ip) + sizeof(*udp) + len;
+  return (ether_output(ifp, eth_len) == eth_len);
 }
 
 static void tx_dhcp(struct mg_tcpip_if *ifp, uint8_t *mac_dst, uint32_t ip_src,
@@ -4801,7 +4803,9 @@ long mg_io_send(struct mg_connection *c, const void *buf, size_t len) {
   uint32_t dst_ip = *(uint32_t *) c->rem.ip;
   len = trim_len(c, len);
   if (c->is_udp) {
-    tx_udp(ifp, s->mac, ifp->ip, c->loc.port, dst_ip, c->rem.port, buf, len);
+    if (!tx_udp(ifp, s->mac, ifp->ip, c->loc.port, dst_ip, c->rem.port, buf,
+                len))
+      return MG_IO_WAIT;
   } else {  // TCP, cap to peer's MSS
     size_t sent;
     if (len > s->dmss) len = s->dmss;  // RFC-6691: reduce if sending opts
@@ -5421,8 +5425,8 @@ bool mg_send(struct mg_connection *c, const void *buf, size_t len) {
   } else if (c->is_udp) {
     struct connstate *s = (struct connstate *) (c + 1);
     len = trim_len(c, len);  // Trimming length if necessary
-    tx_udp(ifp, s->mac, ifp->ip, c->loc.port, rem_ip, c->rem.port, buf, len);
-    res = true;
+    res = tx_udp(ifp, s->mac, ifp->ip, c->loc.port, rem_ip, c->rem.port, buf,
+                 len);
   } else {
     res = mg_iobuf_add(&c->send, c->send.len, buf, len);
   }
diff --git a/src/net_builtin.c b/src/net_builtin.c
index c840d5f9..461a37df 100644
--- a/src/net_builtin.c
+++ b/src/net_builtin.c
@@ -241,12 +241,13 @@ static struct ip *tx_ip(struct mg_tcpip_if *ifp, uint8_t *mac_dst,
   return ip;
 }
 
-static void tx_udp(struct mg_tcpip_if *ifp, uint8_t *mac_dst, uint32_t ip_src,
+static bool tx_udp(struct mg_tcpip_if *ifp, uint8_t *mac_dst, uint32_t ip_src,
                    uint16_t sport, uint32_t ip_dst, uint16_t dport,
                    const void *buf, size_t len) {
   struct ip *ip =
       tx_ip(ifp, mac_dst, 17, ip_src, ip_dst, len + sizeof(struct udp));
   struct udp *udp = (struct udp *) (ip + 1);
+  size_t eth_len;
   // MG_DEBUG(("UDP XX LEN %d %d", (int) len, (int) ifp->tx.len));
   udp->sport = sport;
   udp->dport = dport;
@@ -260,7 +261,8 @@ static void tx_udp(struct mg_tcpip_if *ifp, uint8_t *mac_dst, uint32_t ip_src,
   udp->csum = csumfin(cs);
   memmove(udp + 1, buf, len);
   // MG_DEBUG(("UDP LEN %d %d", (int) len, (int) ifp->frame_len));
-  ether_output(ifp, sizeof(struct eth) + sizeof(*ip) + sizeof(*udp) + len);
+  eth_len = sizeof(struct eth) + sizeof(*ip) + sizeof(*udp) + len;
+  return (ether_output(ifp, eth_len) == eth_len);
 }
 
 static void tx_dhcp(struct mg_tcpip_if *ifp, uint8_t *mac_dst, uint32_t ip_src,
@@ -635,7 +637,9 @@ long mg_io_send(struct mg_connection *c, const void *buf, size_t len) {
   uint32_t dst_ip = *(uint32_t *) c->rem.ip;
   len = trim_len(c, len);
   if (c->is_udp) {
-    tx_udp(ifp, s->mac, ifp->ip, c->loc.port, dst_ip, c->rem.port, buf, len);
+    if (!tx_udp(ifp, s->mac, ifp->ip, c->loc.port, dst_ip, c->rem.port, buf,
+                len))
+      return MG_IO_WAIT;
   } else {  // TCP, cap to peer's MSS
     size_t sent;
     if (len > s->dmss) len = s->dmss;  // RFC-6691: reduce if sending opts
@@ -1255,8 +1259,8 @@ bool mg_send(struct mg_connection *c, const void *buf, size_t len) {
   } else if (c->is_udp) {
     struct connstate *s = (struct connstate *) (c + 1);
     len = trim_len(c, len);  // Trimming length if necessary
-    tx_udp(ifp, s->mac, ifp->ip, c->loc.port, rem_ip, c->rem.port, buf, len);
-    res = true;
+    res = tx_udp(ifp, s->mac, ifp->ip, c->loc.port, rem_ip, c->rem.port, buf,
+                 len);
   } else {
     res = mg_iobuf_add(&c->send, c->send.len, buf, len);
   }