diff --git a/extras/pcf8574/pcf8574.c b/extras/pcf8574/pcf8574.c
index 9e51422..ff9a92c 100644
--- a/extras/pcf8574/pcf8574.c
+++ b/extras/pcf8574/pcf8574.c
@@ -18,7 +18,7 @@ size_t pcf8574_port_read_buf(i2c_dev_t* dev, void *buf, size_t len)
     return len;
 }
 
-size_t pcf8574_port_write_buf(i2c_dev_t* dev, void *buf, size_t len)
+size_t pcf8574_port_write_buf(const i2c_dev_t* dev, void *buf, size_t len)
 {
     if (!len || !buf) return 0;
     uint8_t *_buf = (uint8_t *)buf;
@@ -28,7 +28,7 @@ size_t pcf8574_port_write_buf(i2c_dev_t* dev, void *buf, size_t len)
     return len;
 }
 
-void pcf8574_port_write(i2c_dev_t* dev, uint8_t value)
+void pcf8574_port_write(const i2c_dev_t* dev, uint8_t value)
 {
     i2c_slave_write(dev->bus, dev->addr, NULL, &value, 1);
 }
diff --git a/extras/pcf8574/pcf8574.h b/extras/pcf8574/pcf8574.h
index 742849c..84b6ce0 100644
--- a/extras/pcf8574/pcf8574.h
+++ b/extras/pcf8574/pcf8574.h
@@ -36,7 +36,7 @@ size_t pcf8574_port_read_buf(i2c_dev_t* dev, void *buf, size_t len);
  * \param addr I2C register address (0b0100<A2><A1><A0> for PCF8574)
  * \param value GPIO port value
  */
-void pcf8574_port_write(i2c_dev_t* dev, uint8_t value);
+void pcf8574_port_write(const i2c_dev_t* dev, uint8_t value);
 
 /**
  * \brief Continiously write GPIO values to GPIO port
@@ -45,7 +45,7 @@ void pcf8574_port_write(i2c_dev_t* dev, uint8_t value);
  * @param len Buffer length
  * @return Number of bytes written
  */
-size_t pcf8574_port_write_buf(i2c_dev_t* dev, void *buf, size_t len);
+size_t pcf8574_port_write_buf(const i2c_dev_t* dev, void *buf, size_t len);
 
 /**
  * \brief Read input value of a GPIO pin