diff --git a/lib/frame.js b/lib/frame.js
index 9beb070..40a80b6 100644
--- a/lib/frame.js
+++ b/lib/frame.js
@@ -141,7 +141,7 @@
 		if (data["canvasBlocker-unload"]){
 			enabled = false;
 		}
-		if (data["canvasBlocker-sendNotifications"] === tabId){
+		if (data.hasOwnProperty("canvasBlocker-sendNotifications") && data["canvasBlocker-sendNotifications"] === tabId){
 			browser.runtime.sendMessage({
 				sender: tabId,
 				"canvasBlocker-notifications": notifications