diff --git a/pkg/app/websocket_handlers.go b/pkg/app/websocket_handlers.go
index eba4039..c3b0d09 100644
--- a/pkg/app/websocket_handlers.go
+++ b/pkg/app/websocket_handlers.go
@@ -14,10 +14,21 @@ func processSensorData(babyUID string, sensorData []*client.SensorData, stateMan
 	stateUpdate := baby.State{}
 	for _, sensorDataSet := range sensorData {
 		if *sensorDataSet.SensorType == client.SensorType_TEMPERATURE {
-			stateUpdate.SetTemperatureMilli(*sensorDataSet.ValueMilli)
+			// Nanit occasionally reports -1000000 (-1000 °C) as an invalid-reading
+			// sentinel. Ignore physically impossible values (valid room range
+			// -20..60 °C) so we don't publish garbage to MQTT.
+			if v := *sensorDataSet.ValueMilli; v > -20000 && v < 60000 {
+				stateUpdate.SetTemperatureMilli(v)
+			} else {
+				log.Warn().Int32("valueMilli", v).Str("babyUID", babyUID).Msg("Ignoring out-of-range temperature reading")
+			}
 		}
 		if *sensorDataSet.SensorType == client.SensorType_HUMIDITY {
-			stateUpdate.SetHumidityMilli(*sensorDataSet.ValueMilli)
+			if v := *sensorDataSet.ValueMilli; v >= 0 && v <= 100000 {
+				stateUpdate.SetHumidityMilli(v)
+			} else {
+				log.Warn().Int32("valueMilli", v).Str("babyUID", babyUID).Msg("Ignoring out-of-range humidity reading")
+			}
 		}
 		if *sensorDataSet.SensorType == client.SensorType_NIGHT {
 			stateUpdate.SetIsNight(*sensorDataSet.Value == 1)