diff --git a/README.md b/README.md
index 73bd6f7..7a79920 100644
--- a/README.md
+++ b/README.md
@@ -111,6 +111,13 @@ the original destination with `SO_ORIGINAL_DST`, sends that host:port through th
 encrypted tunnel, and the Windows agent opens the target with a normal outbound
 `TcpClient` from its network position.
 
+The server owns its configured `--listen`/`--port` socket while it is running.
+By default that is `0.0.0.0:443`, so another web server or reverse proxy cannot
+bind port 443 on the same IP at the same time. If you need another service on
+443, either bind PS-Proxy to a different address with `--listen`, run PS-Proxy on
+a different external port with `--port`, or put a fronting load balancer/reverse
+proxy on 443 and forward PS-Proxy traffic to its own backend port.
+
 The server prints a one-time command:
 
 ```powershell
@@ -148,7 +155,11 @@ ldapsearch -x -H ldap://127.0.0.1:1389 -D 'user@example.local' -W -b 'DC=example
 Transparent redirect mode is the recommended test-environment workflow right now.
 The fixed-target relay remains useful when you want a single local port mapped to
 a single target for debugging. Use `--max-streams` to cap concurrent proxied TCP
-connections during high-concurrency tools such as NetExec; the default is 256. When `--dns-listen` and `--dns-target` are set together, the server exposes a UDP DNS listener and forwards raw DNS queries through the enrolled agent to the internal DNS server reachable from the agent host.
+connections during high-concurrency tools such as NetExec; the default is 256.
+When `--dns-listen` and `--dns-target` are set together, the server exposes UDP
+and TCP DNS listeners on the same local address and forwards raw DNS queries
+through the enrolled agent to the internal DNS server reachable from the agent
+host.
 
 ## Security notes
 
diff --git a/agent/PSProxy.Agent/PSProxy.Agent.cs b/agent/PSProxy.Agent/PSProxy.Agent.cs
index e8db9b8..044d079 100644
--- a/agent/PSProxy.Agent/PSProxy.Agent.cs
+++ b/agent/PSProxy.Agent/PSProxy.Agent.cs
@@ -276,24 +276,26 @@ namespace PSProxy.Agent
         {
             if (f.Payload == null) f.Payload = new byte[0];
             if (f.Payload.Length > MaxPayload) throw new InvalidOperationException("frame payload too large");
-            byte[] plainFrame = EncodePlainFrame(f);
-            byte[] seq = U64BE(sendSeq);
-            byte[] plain = Concat(seq, plainFrame);
-            byte[] padded = Pkcs7Pad(plain, 16);
-            byte[] iv = RandomBytes(16);
-            byte[] ct;
-            using (var aes = Aes.Create())
-            {
-                aes.Mode = CipherMode.CBC; aes.Padding = PaddingMode.None; aes.Key = encKey; aes.IV = iv;
-                using (var enc = aes.CreateEncryptor()) { ct = enc.TransformFinalBlock(padded, 0, padded.Length); }
-            }
-            byte[] body = Concat(iv, ct);
-            byte[] tag;
-            using (var h = new HMACSHA256(macKey)) { tag = h.ComputeHash(Concat(seq, body)); }
-            byte[] rec = Concat(body, tag);
-            byte[] len = new byte[4]; WriteI32BE(len, 0, rec.Length);
             lock (sendLock)
             {
+                // The sequence number is part of both plaintext and HMAC input, so
+                // frame construction must be serialized with the write/increment.
+                byte[] plainFrame = EncodePlainFrame(f);
+                byte[] seq = U64BE(sendSeq);
+                byte[] plain = Concat(seq, plainFrame);
+                byte[] padded = Pkcs7Pad(plain, 16);
+                byte[] iv = RandomBytes(16);
+                byte[] ct;
+                using (var aes = Aes.Create())
+                {
+                    aes.Mode = CipherMode.CBC; aes.Padding = PaddingMode.None; aes.Key = encKey; aes.IV = iv;
+                    using (var enc = aes.CreateEncryptor()) { ct = enc.TransformFinalBlock(padded, 0, padded.Length); }
+                }
+                byte[] body = Concat(iv, ct);
+                byte[] tag;
+                using (var h = new HMACSHA256(macKey)) { tag = h.ComputeHash(Concat(seq, body)); }
+                byte[] rec = Concat(body, tag);
+                byte[] len = new byte[4]; WriteI32BE(len, 0, rec.Length);
                 tls.Write(len, 0, len.Length); tls.Write(rec, 0, rec.Length); tls.Flush();
                 sendSeq++;
             }