diff --git a/ampel-firmware/co2_sensor.cpp b/ampel-firmware/co2_sensor.cpp
index efeec4e4b1eae120c08d5baacdc78d41d03d64f3..637ec0a7654b8c0a01a89d5498954e6f928f80c4 100644
--- a/ampel-firmware/co2_sensor.cpp
+++ b/ampel-firmware/co2_sensor.cpp
@@ -291,7 +291,9 @@ namespace sensor {
 
     showState();
 
-    return freshData;
+    // Report data for further processing only if the data is reliable
+    // (state 'READY') or manual calibration is necessary (state 'NEEDS_CALIBRATION').
+    return freshData && (current_state == READY || current_state == NEEDS_CALIBRATION);
   }
 
   /*****************************************************************