diff --git a/lib/sensor_pzem.c b/lib/sensor_pzem.c
index 8565e67..805920f 100644
--- a/lib/sensor_pzem.c
+++ b/lib/sensor_pzem.c
@@ -79,7 +79,7 @@ void sensor_pzem_measurement_request(uint32_t address, enum sensor_pzem_measurem
 	if (tx_i!=0) { // transmission is ongoing
 		return;
 	}
-	if (type>=MAX) { // invalid type
+	if (type>=SENSOR_PZEM_MAX) { // invalid type
 		return;
 	}
 	tx_buffer[0] = 0xB0+type; // set request nibble and type nibble
@@ -107,7 +107,7 @@ struct sensor_pzem_measurement_t sensor_pzem_measurement_decode(void)
 	if ((rx_buffer[0]&0xf0)!=0xa0) { // not a response received
 		return measurement;
 	}
-	if ((rx_buffer[0]&0x0f)>=MAX) { // not a valid response type received (actually 4 and 5 are valid, but should not happen when using this code
+	if ((rx_buffer[0]&0x0f)>=SENSOR_PZEM_MAX) { // not a valid response type received (actually 4 and 5 are valid, but should not happen when using this code
 		return measurement;
 	}
 	uint8_t checksum = 0; // calculate checksum (sum of all other bytes)
@@ -120,16 +120,16 @@ struct sensor_pzem_measurement_t sensor_pzem_measurement_decode(void)
 	measurement.valid = true; // all checks passed
 	measurement.type = rx_buffer[0]&0x0f; // save type
 	switch (measurement.type) { // decode value depending on type
-		case VOLTAGE:
+		case SENSOR_PZEM_VOLTAGE:
 			measurement.value.voltage = ((uint16_t)rx_buffer[1]<<8)+rx_buffer[2]+rx_buffer[3]*0.1;
 			break;
-		case CURRENT:
+		case SENSOR_PZEM_CURRENT:
 			measurement.value.current = rx_buffer[2]+rx_buffer[3]/100;
 			break;
-		case POWER:
+		case SENSOR_PZEM_POWER:
 			measurement.value.power = ((uint16_t)rx_buffer[1]<<8)+rx_buffer[2];
 			break;
-		case ENERGY:
+		case SENSOR_PZEM_ENERGY:
 			measurement.value.power = ((uint32_t)rx_buffer[1]<<16)+((uint16_t)rx_buffer[2]<<8)+rx_buffer[3];
 			break;
 		default:
diff --git a/lib/sensor_pzem.h b/lib/sensor_pzem.h
index abbf5df..dd7b381 100644
--- a/lib/sensor_pzem.h
+++ b/lib/sensor_pzem.h
@@ -25,11 +25,11 @@ extern volatile bool sensor_pzem_measurement_received;
 
 /** measurements offered by electricity meter */
 enum sensor_pzem_measurement_type_t {
-	VOLTAGE = 0,
-	CURRENT = 1,
-	POWER = 2,
-	ENERGY = 3,
-	MAX
+	SENSOR_PZEM_VOLTAGE = 0,
+	SENSOR_PZEM_CURRENT = 1,
+	SENSOR_PZEM_POWER = 2,
+	SENSOR_PZEM_ENERGY = 3,
+	SENSOR_PZEM_MAX
 };
 
 /** measurement returned by electricity meter */
diff --git a/main.c b/main.c
index 318cf64..5fdd6d9 100644
--- a/main.c
+++ b/main.c
@@ -170,7 +170,7 @@ void main(void)
 	sensor_pzem_setup(); // setup PZEM electricity meter
 	printf("OK\n");
 
-	sensor_pzem_measurement_request(0xc0a80101, VOLTAGE);
+	sensor_pzem_measurement_request(0xc0a80101, SENSOR_PZEM_VOLTAGE);
 
 	// main loop
 	printf("command input: ready\n");
@@ -212,16 +212,16 @@ void main(void)
 			struct sensor_pzem_measurement_t measurement = sensor_pzem_measurement_decode(); // decode measurement
 			if (measurement.valid) { // only show valid measurement
 				switch (measurement.type) {
-				case VOLTAGE:
+				case SENSOR_PZEM_VOLTAGE:
 					printf("voltage: %.01f V\n", measurement.value.voltage);
 					break;
-				case CURRENT:
+				case SENSOR_PZEM_CURRENT:
 					printf("current: %.02f A\n", measurement.value.current);
 					break;
-				case POWER:
+				case SENSOR_PZEM_POWER:
 					printf("power: %.00f W\n", measurement.value.power);
 					break;
-				case ENERGY:
+				case SENSOR_PZEM_ENERGY:
 					printf("energy: %lu Wh\n", measurement.value.energy);
 					break;
 				default: