diff --git a/index.bs b/index.bs
index 80eaae5..a80813d 100644
--- a/index.bs
+++ b/index.bs
@@ -895,7 +895,7 @@ partial interface DedicatedWorkerGlobalScope {
 interface RTCRtpScriptTransformer : EventTarget {
     // Attributes and methods related to the transformer source
     readonly attribute ReadableStream readable;
-    Promise<unsigned long long> generateKeyFrame(optional DOMString rid);
+    Promise<undefined> generateKeyFrame(optional DOMString rid);
     Promise<undefined> sendKeyFrameRequest();
     // Attributes and methods related to the transformer sink
     readonly attribute WritableStream writable;
@@ -1024,7 +1024,7 @@ For any {{RTCRtpScriptTransformer}} named |transformer|, the following steps are
 1. For each |task| in |encoder|.`[[pendingKeyFrameTasks]]`, run the following steps:
     1. If |frame| was generated by a video encoder identified by |task|.`[[rid]]`, run the following steps:
         1. Remove |task| from |encoder|.`[[pendingKeyFrameTasks]]`.
-        1. Resolve |task|.`[[promise]]` with |frame|'s timestamp.
+        1. Resolve |task|.`[[promise]]` with undefined.
 
 By resolving the promises just before enqueuing the corresponding key frame in a {{RTCRtpScriptTransformer}}'s readable,
 the resolution callbacks of the promises are always executed just before the corresponding key frame is exposed.