diff --git a/src/modbus.h b/src/modbus.h
index e3e9f86..7a9275f 100755
--- a/src/modbus.h
+++ b/src/modbus.h
@@ -202,6 +202,7 @@ MODBUS_API const char *modbus_strerror(int errnum);
 MODBUS_API int modbus_read_bits(modbus_t *ctx, int addr, int nb, uint8_t *dest);
 MODBUS_API int modbus_read_input_bits(modbus_t *ctx, int addr, int nb, uint8_t *dest);
 MODBUS_API int modbus_read_registers(modbus_t *ctx, int addr, int nb, uint16_t *dest);
+MODBUS_API int modbus_communication_transparent(modbus_t *ctx, char *buf, int len, char *dest);
 MODBUS_API int modbus_read_input_registers(modbus_t *ctx, int addr, int nb, uint16_t *dest);
 MODBUS_API int modbus_write_bit(modbus_t *ctx, int coil_addr, int status);
 MODBUS_API int modbus_write_register(modbus_t *ctx, int reg_addr, int value);