diff --git a/twitch-ad-countdown-timer/script.js b/twitch-ad-countdown-timer/script.js
index 7d3b993..bae7b05 100644
--- a/twitch-ad-countdown-timer/script.js
+++ b/twitch-ad-countdown-timer/script.js
@@ -146,7 +146,7 @@ client.on('Twitch.UpcomingAd', (response) => {
 /////////////////////
 
 function TwitchAdRun(data) {
-	const duration = data.length_seconds;
+	const duration = data.lengthSeconds ?? data.length_seconds;
 
 	// Unset the upcoming ad countdown warning
 	upcomingAdWarningStartDelay = null;