diff --git a/code/b-parasite/src/prst/adc.c b/code/b-parasite/src/prst/adc.c
index 01a7115..de57482 100644
--- a/code/b-parasite/src/prst/adc.c
+++ b/code/b-parasite/src/prst/adc.c
@@ -134,6 +134,11 @@ prst_adc_soil_moisture_t prst_adc_soil_read(double battery_voltage) {
 prst_adc_photo_sensor_t prst_adc_photo_read(double battery_voltage) {
   nrf_saadc_value_t raw_photo_output =
       sample_adc_channel(PRST_ADC_PHOTO_CHANNEL);
+
+  if (raw_photo_output < 0) {
+    raw_photo_output = 0;
+  }
+
   prst_adc_photo_sensor_t ret;
   ret.raw = raw_photo_output;
   ret.voltage = (3.6 * raw_photo_output) / (1 << PRST_ADC_RESOLUTION);
@@ -161,4 +166,4 @@ prst_adc_photo_sensor_t prst_adc_photo_read(double battery_voltage) {
                ret.brightness);
 #endif
   return ret;
-}
\ No newline at end of file
+}