diff --git a/SerialPort.cpp b/SerialPort.cpp
index 75c7309..5fac49a 100644
--- a/SerialPort.cpp
+++ b/SerialPort.cpp
@@ -357,6 +357,11 @@ void SerialPort::process()
                     }
                     break;
 
+                /** DFSI */
+                case CMD_DFSI_DATA:
+                    sendNAK(RSN_INVALID_REQUEST);
+                    break;
+
                 default:
                     // Handle this, send a NAK back
                     sendNAK(RSN_NAK);
diff --git a/SerialPort.h b/SerialPort.h
index b788bee..877b2b3 100644
--- a/SerialPort.h
+++ b/SerialPort.h
@@ -92,6 +92,8 @@ enum DVM_COMMANDS {
     CMD_P25_LOST = 0x32U,
     CMD_P25_CLEAR = 0x33U,
 
+    CMD_DFSI_DATA = 0x40U,
+
     CMD_ACK = 0x70U,
     CMD_NAK = 0x7FU,