diff --git a/SerialPort.cpp b/SerialPort.cpp
index e0d6193..dc05f13 100644
--- a/SerialPort.cpp
+++ b/SerialPort.cpp
@@ -68,6 +68,8 @@ const uint8_t MMDVM_NAK          = 0x7FU;
 
 const uint8_t MMDVM_SERIAL       = 0x80U;
 
+const uint8_t MMDVM_TRANSPARENT  = 0x90U;
+
 const uint8_t MMDVM_DEBUG1       = 0xF1U;
 const uint8_t MMDVM_DEBUG2       = 0xF2U;
 const uint8_t MMDVM_DEBUG3       = 0xF3U;
@@ -759,6 +761,10 @@ void CSerialPort::process()
             }
             break;
 
+          case MMDVM_TRANSPARENT:
+            // Do nothing on the MMDVM.
+            break;
+
 #if defined(SERIAL_REPEATER)
           case MMDVM_SERIAL: {
             for (uint8_t i = 3U; i < m_len; i++)