diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index bd515ce..9381f71 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -164,6 +164,19 @@ SYSCTL_INT(_net_inet_tcp_experimental, OID_AUTO, initcwnd10, CTLFLAG_VNET | CTLF
     &VNET_NAME(tcp_do_initcwnd10), 0,
     "Enable RFC 6928 (Increasing initial CWND to 10)");
 
+SYSCTL_NODE(_net_inet_tcp, OID_AUTO, nonstandard, CTLFLAG_RW, 0,
+    "Nonstandard TCP extensions");
+
+VNET_DEFINE(int, tcp_nonstandard_allowed) = 0;
+SYSCTL_INT(_net_inet_tcp_nonstandard, OID_AUTO, allowed, CTLFLAG_VNET | CTLFLAG_RW,
+    &VNET_NAME(tcp_nonstandard_allowed), 0,
+    "Allow nonstandard TCP extensions");
+
+VNET_DEFINE(int, tcp_nonstandard_initcwnd) = 0;
+SYSCTL_INT(_net_inet_tcp_nonstandard, OID_AUTO, initcwnd, CTLFLAG_VNET | CTLFLAG_RW,
+    &VNET_NAME(tcp_nonstandard_initcwnd), 0,
+    "Slow-start flight size (initial congestion window)");
+
 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_do_rfc3465), 0,
@@ -361,6 +374,7 @@ cc_conn_init(struct tcpcb *tp)
         * RFC5681 Section 3.1 specifies the default conservative values.
         * RFC3390 specifies slightly more aggressive values.
         * RFC6928 increases it to ten segments.
+        * Support for user specified value for flight size.
         *
         * If a SYN or SYN/ACK was lost and retransmitted, we have to
         * reduce the initial CWND to one segment as congestion is likely
@@ -368,6 +382,9 @@ cc_conn_init(struct tcpcb *tp)
         */
        if (tp->snd_cwnd == 1)
                tp->snd_cwnd = tp->t_maxseg;            /* SYN(-ACK) lost */
+       else if (V_tcp_nonstandard_allowed && V_tcp_nonstandard_initcwnd)
+               tp->snd_cwnd = min(V_tcp_nonstandard_initcwnd * tp->t_maxseg,
+                   max(2 * tp->t_maxseg, V_tcp_nonstandard_initcwnd * 1460));
        else if (V_tcp_do_initcwnd10)
                tp->snd_cwnd = min(10 * tp->t_maxseg,
                    max(2 * tp->t_maxseg, 14600));
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index df01735..96742c4 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -614,6 +614,8 @@ VNET_DECLARE(int, tcp_minmss);
 VNET_DECLARE(int, tcp_delack_enabled);
 VNET_DECLARE(int, tcp_do_rfc3390);
 VNET_DECLARE(int, tcp_do_initcwnd10);
+VNET_DECLARE(int, tcp_nonstandard_allowed);
+VNET_DECLARE(int, tcp_nonstandard_initcwnd);
 VNET_DECLARE(int, tcp_sendspace);
 VNET_DECLARE(int, tcp_recvspace);
 VNET_DECLARE(int, path_mtu_discovery);
@@ -626,6 +628,8 @@ VNET_DECLARE(int, tcp_abc_l_var);
 #define        V_tcp_delack_enabled    VNET(tcp_delack_enabled)
 #define        V_tcp_do_rfc3390        VNET(tcp_do_rfc3390)
 #define        V_tcp_do_initcwnd10     VNET(tcp_do_initcwnd10)
+#define        V_tcp_nonstandard_allowed       VNET(tcp_nonstandard_allowed)
+#define        V_tcp_nonstandard_initcwnd      VNET(tcp_nonstandard_initcwnd)
 #define        V_tcp_sendspace         VNET(tcp_sendspace)
 #define        V_tcp_recvspace         VNET(tcp_recvspace)
 #define        V_path_mtu_discovery    VNET(path_mtu_discovery)