diff --git a/net/tcp/tcp_conn.c b/net/tcp/tcp_conn.c
index b6d3d95841a..6890d6128e4 100644
--- a/net/tcp/tcp_conn.c
+++ b/net/tcp/tcp_conn.c
@@ -1153,7 +1153,7 @@ FAR struct tcp_conn_s *tcp_alloc_accept(FAR struct net_driver_s *dev,
       conn->expired          = 0;
       conn->isn              = 0;
       conn->sent             = 0;
-      conn->sndseq_max       = tcp_getsequence(conn->sndseq);
+      conn->sndseq_max       = tcp_getsequence(conn->sndseq) + 1;
 #endif
 
 #ifdef CONFIG_NET_TCP_CC_NEWRENO
@@ -1465,7 +1465,7 @@ int tcp_connect(FAR struct tcp_conn_s *conn, FAR const struct sockaddr *addr)
   conn->expired    = 0;
   conn->isn        = 0;
   conn->sent       = 0;
-  conn->sndseq_max = tcp_getsequence(conn->sndseq);
+  conn->sndseq_max = tcp_getsequence(conn->sndseq) + 1;
 #endif
 
   /* Save initial sndseq to rexmit_seq, otherwise it will be zero */
diff --git a/net/tcp/tcp_input.c b/net/tcp/tcp_input.c
index 46f035ae2a6..e9c51f793e5 100644
--- a/net/tcp/tcp_input.c
+++ b/net/tcp/tcp_input.c
@@ -1056,7 +1056,9 @@ found:
            * bytes
            */
 
-          /* RFC793,p72~p73 In states from ESTABLISHED to LASTACK:"If the
+          /* RFC793, p72~p73 1) In SYN-RCVD state, if the ACK is not
+           * acceptable, send a reset.
+           * 2)In states from ESTABLISHED to LASTACK:"If the
            * ACK acks something not yet sent (SEG.ACK > SND.NXT) then send
            * an ACK, drop the segment, and return."
            */
@@ -1067,6 +1069,10 @@ found:
               tcp_send(dev, conn, TCP_ACK, tcpiplen);
               return;
             }
+          else if ((conn->tcpstateflags & TCP_STATE_MASK) == TCP_SYN_RCVD)
+            {
+              goto reset;
+            }
         }
 
       if (lasttxunacked == 0)