diff --git a/AdaptiveBrightness/main_window.cpp b/AdaptiveBrightness/main_window.cpp
index 93d33e4..8a88d37 100644
--- a/AdaptiveBrightness/main_window.cpp
+++ b/AdaptiveBrightness/main_window.cpp
@@ -298,7 +298,9 @@ void MainWindow::updateState()
 
         bool errorOccurred = false;
         for(auto& monitor: m_monitors) {
-            monitor.brightness = monitor.manualOverride ? monitor.brightness : brightness;
+            if(!std::isnan(brightness) && !monitor.manualOverride) {
+                monitor.brightness = brightness;
+            }
             if(!monitor.driver.setBrightness(monitor.brightness)) {
                 errorOccurred = true;
             }
@@ -306,7 +308,7 @@ void MainWindow::updateState()
         return !errorOccurred;
     };
 
-    auto brightness = 0.5f;
+    auto brightness = NAN;
 
     if(!getAverageSensorValue(brightness)) {
         enumSensors();