diff --git a/lib/default/TasmotaSerial-3.3.0/src/TasmotaSerial.h b/lib/default/TasmotaSerial-3.3.0/src/TasmotaSerial.h
index 3a90626fe..c4795a608 100644
--- a/lib/default/TasmotaSerial-3.3.0/src/TasmotaSerial.h
+++ b/lib/default/TasmotaSerial-3.3.0/src/TasmotaSerial.h
@@ -35,6 +35,7 @@
 #include <HardwareSerial.h>
 #endif
 
+extern uint32_t ConvertSerialConfig(uint8_t serial_config);
 class TasmotaSerial : public Stream {
   public:
     TasmotaSerial(int receive_pin, int transmit_pin, int hardware_fallback = 0, int nwmode = 0, int buffer_size = TM_SERIAL_BUFFER_SIZE);