diff --git a/Adafruit_I2CDevice.cpp b/Adafruit_I2CDevice.cpp
index eea3187..33d3115 100644
--- a/Adafruit_I2CDevice.cpp
+++ b/Adafruit_I2CDevice.cpp
@@ -66,8 +66,8 @@ bool Adafruit_I2CDevice::detected(void) {
  *    @param  stop Whether to send an I2C STOP signal on write
  *    @return True if write was successful, otherwise false.
  */
-bool Adafruit_I2CDevice::write(uint8_t *buffer, size_t len, bool stop,
-                               uint8_t *prefix_buffer, size_t prefix_len) {
+bool Adafruit_I2CDevice::write(const uint8_t *buffer, size_t len, bool stop,
+                               const uint8_t *prefix_buffer, size_t prefix_len) {
   if ((len + prefix_len) > maxBufferSize()) {
     // currently not guaranteed to work if more than 32 bytes!
     // we will need to find out if some platforms have larger
@@ -200,7 +200,7 @@ bool Adafruit_I2CDevice::read(uint8_t *buffer, size_t len, bool stop) {
  *    @param  stop Whether to send an I2C STOP signal between the write and read
  *    @return True if write & read was successful, otherwise false.
  */
-bool Adafruit_I2CDevice::write_then_read(uint8_t *write_buffer,
+bool Adafruit_I2CDevice::write_then_read(const uint8_t *write_buffer,
                                          size_t write_len, uint8_t *read_buffer,
                                          size_t read_len, bool stop) {
   if (!write(write_buffer, write_len, stop)) {
diff --git a/Adafruit_I2CDevice.h b/Adafruit_I2CDevice.h
index 0dcfc50..28468ea 100644
--- a/Adafruit_I2CDevice.h
+++ b/Adafruit_I2CDevice.h
@@ -12,9 +12,9 @@ public:
   bool detected(void);
 
   bool read(uint8_t *buffer, size_t len, bool stop = true);
-  bool write(uint8_t *buffer, size_t len, bool stop = true,
-             uint8_t *prefix_buffer = NULL, size_t prefix_len = 0);
-  bool write_then_read(uint8_t *write_buffer, size_t write_len,
+  bool write(const uint8_t *buffer, size_t len, bool stop = true,
+             const uint8_t *prefix_buffer = NULL, size_t prefix_len = 0);
+  bool write_then_read(const uint8_t *write_buffer, size_t write_len,
                        uint8_t *read_buffer, size_t read_len,
                        bool stop = false);
   bool setSpeed(uint32_t desiredclk);