diff --git a/custom-idl/webrtc-encoded-transform.idl b/custom-idl/webrtc-encoded-transform.idl
new file mode 100644
index 000000000..b11973415
--- /dev/null
+++ b/custom-idl/webrtc-encoded-transform.idl
@@ -0,0 +1,7 @@
+// https://github.com/w3c/webrtc-encoded-transform/pull/64
+partial interface RTCRtpSender {
+  RTCInsertableStreams createEncodedStreams();
+};
+partial interface RTCRtpReceiver {
+  RTCInsertableStreams createEncodedStreams();
+};