diff --git a/ampel-firmware/ampel-firmware.ino b/ampel-firmware/ampel-firmware.ino
index 3fdc1d1c5f6f9b290c6e00edc6dc8b897c57b8fb..bf673706f3acfa69386ed1c48c0e8e81f70a935f 100644
--- a/ampel-firmware/ampel-firmware.ino
+++ b/ampel-firmware/ampel-firmware.ino
@@ -141,7 +141,12 @@ void loop() {
   keepServicesAlive();
 
   // Short press for night mode, Long press for calibration.
-  checkFlashButton();
+  // Inactive during calibration.
+  if (!(sensor::current_state == sensor::PREPARE_CALIBRATION_STABLE ||
+        sensor::current_state == sensor::PREPARE_CALIBRATION_UNSTABLE))
+  {
+    checkFlashButton();
+  }
 
   checkSerialInput();