diff --git a/src/GoogleCloudPubSub/GoogleCloudPubSub.ts b/src/GoogleCloudPubSub/GoogleCloudPubSub.ts
index 23c4660..cbd3704 100644
--- a/src/GoogleCloudPubSub/GoogleCloudPubSub.ts
+++ b/src/GoogleCloudPubSub/GoogleCloudPubSub.ts
@@ -139,7 +139,7 @@ export class GoogleCloudPubSub implements GCPubSub {
       );
 
       if (opts.options?.autoAck !== false) {
-        message.ack();
+        extendedMessage.ack();
       }
 
       if (opts.onMessage !== undefined) {