diff --git a/mongoose.c b/mongoose.c
index 76c8bd16..2e2bf41e 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -4502,13 +4502,13 @@ static void rx_tcp(struct mg_tcpip_if *ifp, struct pkt *pkt) {
 #if 0
   MG_INFO(("%lu %hhu %d", c ? c->id : 0, pkt->tcp->flags, (int) pkt->pay.len));
 #endif
-  if (c != NULL && c->is_connecting && pkt->tcp->flags & (TH_SYN | TH_ACK)) {
+  if (c != NULL && c->is_connecting && pkt->tcp->flags == (TH_SYN | TH_ACK)) {
     s->seq = mg_ntohl(pkt->tcp->ack), s->ack = mg_ntohl(pkt->tcp->seq) + 1;
     tx_tcp_pkt(ifp, pkt, TH_ACK, pkt->tcp->ack, NULL, 0);
     c->is_connecting = 0;  // Client connected
     settmout(c, MIP_TTYPE_KEEPALIVE);
     mg_call(c, MG_EV_CONNECT, NULL);  // Let user know
-  } else if (c != NULL && c->is_connecting) {
+  } else if (c != NULL && c->is_connecting && pkt->tcp->flags != TH_ACK) {
     // mg_hexdump(pkt->raw.ptr, pkt->raw.len);
     tx_tcp_pkt(ifp, pkt, TH_RST | TH_ACK, pkt->tcp->ack, NULL, 0);
   } else if (c != NULL && pkt->tcp->flags & TH_RST) {
diff --git a/src/net_builtin.c b/src/net_builtin.c
index 01268fde..5f4caa9b 100644
--- a/src/net_builtin.c
+++ b/src/net_builtin.c
@@ -677,13 +677,13 @@ static void rx_tcp(struct mg_tcpip_if *ifp, struct pkt *pkt) {
 #if 0
   MG_INFO(("%lu %hhu %d", c ? c->id : 0, pkt->tcp->flags, (int) pkt->pay.len));
 #endif
-  if (c != NULL && c->is_connecting && pkt->tcp->flags & (TH_SYN | TH_ACK)) {
+  if (c != NULL && c->is_connecting && pkt->tcp->flags == (TH_SYN | TH_ACK)) {
     s->seq = mg_ntohl(pkt->tcp->ack), s->ack = mg_ntohl(pkt->tcp->seq) + 1;
     tx_tcp_pkt(ifp, pkt, TH_ACK, pkt->tcp->ack, NULL, 0);
     c->is_connecting = 0;  // Client connected
     settmout(c, MIP_TTYPE_KEEPALIVE);
     mg_call(c, MG_EV_CONNECT, NULL);  // Let user know
-  } else if (c != NULL && c->is_connecting) {
+  } else if (c != NULL && c->is_connecting && pkt->tcp->flags != TH_ACK) {
     // mg_hexdump(pkt->raw.ptr, pkt->raw.len);
     tx_tcp_pkt(ifp, pkt, TH_RST | TH_ACK, pkt->tcp->ack, NULL, 0);
   } else if (c != NULL && pkt->tcp->flags & TH_RST) {