diff --git a/ampel-firmware/co2_sensor.cpp b/ampel-firmware/co2_sensor.cpp
index 895e9614fa99961c0fbbf904a36706657a70041c..f17e0f7d5f9607cd579abf2583d1644f696c9c9d 100644
--- a/ampel-firmware/co2_sensor.cpp
+++ b/ampel-firmware/co2_sensor.cpp
@@ -235,10 +235,10 @@ namespace sensor {
       temperature = scd30.getTemperature();
       humidity = scd30.getHumidity();
 
-      if (co2 <= 0) {
+      if (co2 == 0) {
         // NOTE: Data is available, but it's sometimes erroneous: the sensor outputs
         // zero ppm but non-zero temperature and non-zero humidity.
-        Serial.println(F("Invalid sensor data - CO2 concentration <= 0 ppm"));
+        Serial.println(F("Invalid sensor data - CO2 concentration supposedly 0 ppm"));
         switchState(BOOTUP);
       } else if ((current_state == PREPARE_CALIBRATION_UNSTABLE) || (current_state == PREPARE_CALIBRATION_STABLE)) {
         // Check for pre-calibration states first, because we do not want to