diff --git a/libraries/AP_TemperatureSensor/TSYS01.cpp b/libraries/AP_TemperatureSensor/TSYS01.cpp
index 730febfb1b..9a16ff3e29 100644
--- a/libraries/AP_TemperatureSensor/TSYS01.cpp
+++ b/libraries/AP_TemperatureSensor/TSYS01.cpp
@@ -53,7 +53,7 @@ bool TSYS01::init(uint8_t bus)
     return true;
 }
 
-bool TSYS01::_reset()
+bool TSYS01::_reset() const
 {
     return _dev->transfer(&TSYS01_CMD_RESET, 1, nullptr, 0);
 }
@@ -80,7 +80,7 @@ bool TSYS01::_read_prom()
 }
 
 // Borrowed from MS Baro driver
-uint16_t TSYS01::_read_prom_word(uint8_t word)
+uint16_t TSYS01::_read_prom_word(uint8_t word) const
 {
     const uint8_t reg = TSYS01_CMD_READ_PROM + (word << 1);
     uint8_t val[2];
@@ -90,12 +90,12 @@ uint16_t TSYS01::_read_prom_word(uint8_t word)
     return (val[0] << 8) | val[1];
 }
 
-bool TSYS01::_convert()
+bool TSYS01::_convert() const
 {
     return _dev->transfer(&TSYS01_CMD_CONVERT, 1, nullptr, 0);
 }
 
-uint32_t TSYS01::_read_adc()
+uint32_t TSYS01::_read_adc() const
 {
     uint8_t val[3];
     if (!_dev->transfer(&TSYS01_CMD_READ_ADC, 1, val, 3)) {
diff --git a/libraries/AP_TemperatureSensor/TSYS01.h b/libraries/AP_TemperatureSensor/TSYS01.h
index 6ded0190c1..9c93067330 100644
--- a/libraries/AP_TemperatureSensor/TSYS01.h
+++ b/libraries/AP_TemperatureSensor/TSYS01.h
@@ -14,8 +14,8 @@ class TSYS01 {
 public:
 
     bool init(uint8_t bus);
-    float temperature(void) { return _temperature; } // temperature in degrees C
-    bool healthy(void) { // do we have a valid temperature reading?
+    float temperature(void) const { return _temperature; } // temperature in degrees C
+    bool healthy(void) const { // do we have a valid temperature reading?
         return _healthy;
     }
 
@@ -25,11 +25,11 @@ private:
     float _temperature; // degrees C
     bool _healthy; // we have a valid temperature reading to report
     uint16_t _k[5]; // internal calibration for temperature calculation
-    bool _reset(void); // reset device
+    bool _reset(void) const; // reset device
     bool _read_prom(void); // read (relevant) internal calibration registers into _k
-    bool _convert(void); // begin an ADC conversion (min:7.40ms typ:8.22ms max:9.04ms)
-    uint32_t _read_adc(void);
-    uint16_t _read_prom_word(uint8_t word);
+    bool _convert(void) const; // begin an ADC conversion (min:7.40ms typ:8.22ms max:9.04ms)
+    uint32_t _read_adc(void) const;
+    uint16_t _read_prom_word(uint8_t word) const;
     void _timer(void); // update the temperature, called at 20Hz
     void _calculate(uint32_t adc); // calculate temperature using adc reading and internal calibration
 };