diff --git a/pttyhandler.cpp b/pttyhandler.cpp
index d709de1..63b272a 100644
--- a/pttyhandler.cpp
+++ b/pttyhandler.cpp
@@ -189,6 +189,18 @@ void pttyHandler::receiveDataIn(int fd) {
             port->commitTransaction();
 #endif
 
+            int lastFE = inPortData.lastIndexOf((char)0xfe);
+            if (civId == 0 && inPortData.length() > lastFE + 2 && (quint8)inPortData[lastFE + 2] > (quint8)0xdf && (quint8)inPortData[lastFE + 2] < (quint8)0xef) {
+                // This is (should be) the remotes CIV id.
+                civId = (quint8)inPortData[lastFE + 2];
+                qDebug(logSerial()) << "pty detected remote CI-V:" << hex << civId;
+            }
+            else if (civId != 0 && inPortData.length() > lastFE + 2 && (quint8)inPortData[lastFE + 2] != civId)
+            {
+                civId = (quint8)inPortData[lastFE + 2];
+                qDebug(logSerial()) << "pty remote CI-V changed:" << hex << (quint8)civId;
+            }
+
             // filter 1A 05 01 12/27 = C-IV transceive command before forwarding on.
             if (inPortData.contains(QByteArrayLiteral("\x1a\x05\x01\x12")) || inPortData.contains(QByteArrayLiteral("\x1a\x05\x01\x27")))
             {
@@ -200,7 +212,7 @@ void pttyHandler::receiveDataIn(int fd) {
                 sendDataOut(inPortData); // Echo command back
                 sendDataOut(reply);
             }
-            else
+            else if (inPortData.length() > lastFE + 2 && ((quint8)inPortData[lastFE + 1] == civId || (quint8)inPortData[lastFE + 2] == civId))
             {
                 emit haveDataFromPort(inPortData);
                 //qDebug(logSerial()) << "Data from pseudo term:";
diff --git a/pttyhandler.h b/pttyhandler.h
index c066df2..ac96684 100644
--- a/pttyhandler.h
+++ b/pttyhandler.h
@@ -67,7 +67,7 @@ private:
     void printHex(const QByteArray& pdata, bool printVert, bool printHoriz);
 
     QSocketNotifier *ptReader = nullptr;
-
+    quint8 civId=0;
 };
 
 #endif // PTTYHANDLER_H