diff --git a/core/dive.c b/core/dive.c
index 351476bb8..36b1376fa 100644
--- a/core/dive.c
+++ b/core/dive.c
@@ -1657,9 +1657,10 @@ static void sample_renumber(struct sample *s, int i, const int mapping[])
 	int j;
 
 	for (j = 0; j < MAX_SENSORS; j++) {
-		int sensor;
+		int sensor = -1;
 
-		sensor = mapping[s->sensor[j]];
+		if (s->sensor[j] != NO_SENSOR)
+			sensor = mapping[s->sensor[j]];
 		if (sensor == -1) {
 			// Remove sensor and gas pressure info
 			if (i == 0) {
diff --git a/core/profile.c b/core/profile.c
index d20d068e3..2db4c54c3 100644
--- a/core/profile.c
+++ b/core/profile.c
@@ -566,9 +566,9 @@ static void populate_plot_entries(const struct dive *dive, const struct divecomp
 		} else {
 			entry->pressures.o2 = sample->setpoint.mbar / 1000.0;
 		}
-		if (sample->pressure[0].mbar)
+		if (sample->pressure[0].mbar && sample->sensor[0] != NO_SENSOR)
 			set_plot_pressure_data(pi, idx, SENSOR_PR, sample->sensor[0], sample->pressure[0].mbar);
-		if (sample->pressure[1].mbar)
+		if (sample->pressure[1].mbar && sample->sensor[1] != NO_SENSOR)
 			set_plot_pressure_data(pi, idx, SENSOR_PR, sample->sensor[1], sample->pressure[1].mbar);
 		if (sample->temperature.mkelvin)
 			entry->temperature = lasttemp = sample->temperature.mkelvin;
diff --git a/core/sample.h b/core/sample.h
index 75c7bb1b4..1732b4d02 100644
--- a/core/sample.h
+++ b/core/sample.h
@@ -9,6 +9,8 @@ extern "C" {
 #endif
 
 #define MAX_SENSORS 2
+#define NO_SENSOR ((uint8_t)-1)
+
 struct sample                         // BASE TYPE BYTES  UNITS    RANGE               DESCRIPTION
 {                                     // --------- -----  -----    -----               -----------
 	duration_t time;                  // int32_t    4  seconds  (0-34 yrs)             elapsed dive time up to this sample
@@ -23,7 +25,7 @@ struct sample                         // BASE TYPE BYTES  UNITS    RANGE
 	o2pressure_t setpoint;            // uint16_t   2    mbar   (0-65 bar)             O2 partial pressure (will be setpoint)
 	o2pressure_t o2sensor[3];         // uint16_t   6    mbar   (0-65 bar)             Up to 3 PO2 sensor values (rebreather)
 	bearing_t bearing;                // int16_t    2  degrees  (-1 no val, 0-360 deg) compass bearing
-	uint8_t sensor[MAX_SENSORS];      // uint8_t    1  sensorID (0-255)                ID of cylinder pressure sensor
+	uint8_t sensor[MAX_SENSORS];      // uint8_t    1  sensorID (0-254)                ID of cylinder pressure sensor
 	uint16_t cns;                     // uint16_t   1     %     (0-64k %)              cns% accumulated
 	uint8_t heartbeat;                // uint8_t    1  beats/m  (0-255)                heart rate measurement
 	volume_t sac;                     //            4  ml/min                          predefined SAC