diff --git a/inputfiles/addedTypes.jsonc b/inputfiles/addedTypes.jsonc
index e377c9546..5186b40c7 100644
--- a/inputfiles/addedTypes.jsonc
+++ b/inputfiles/addedTypes.jsonc
@@ -314,32 +314,6 @@
                     }
                 }
             },
-            // The spec removed `timestamp` but browsers still have it.
-            // https://github.com/w3c/webrtc-encoded-transform/pull/204
-            "RTCEncodedAudioFrame": {
-                "properties": {
-                    "property": {
-                        "timestamp": {
-                            "mdnUrl": "https://developer.mozilla.org/docs/Web/API/RTCEncodedAudioFrame/timestamp",
-                            "name": "timestamp",
-                            "type": "long long",
-                            "readonly": true
-                        }
-                    }
-                }
-            },
-            "RTCEncodedVideoFrame": {
-                "properties": {
-                    "property": {
-                        "timestamp": {
-                            "mdnUrl": "https://developer.mozilla.org/docs/Web/API/RTCEncodedVideoFrame/timestamp",
-                            "name": "timestamp",
-                            "type": "long long",
-                            "readonly": true
-                        }
-                    }
-                }
-            },
             "RuntimeError": {
                 "name": "RuntimeError",
                 "extends": "Error",
diff --git a/inputfiles/patches/webrtc-encoded-transform.kdl b/inputfiles/patches/webrtc-encoded-transform.kdl
index 16d090dc7..6c3bc9746 100644
--- a/inputfiles/patches/webrtc-encoded-transform.kdl
+++ b/inputfiles/patches/webrtc-encoded-transform.kdl
@@ -1,5 +1,15 @@
 // https://w3c.github.io/webrtc-encoded-transform/
 
+// The spec removed `timestamp` but browsers still have it as of 2025-12
+// https://github.com/w3c/webrtc-encoded-transform/pull/204
+interface RTCEncodedAudioFrame {
+  property timestamp type="long long" readonly=#true mdnUrl="https://developer.mozilla.org/docs/Web/API/RTCEncodedAudioFrame/timestamp"
+}
+
+interface RTCEncodedVideoFrame {
+  property timestamp type="long long" readonly=#true mdnUrl="https://developer.mozilla.org/docs/Web/API/RTCEncodedVideoFrame/timestamp"
+}
+
 removals {
   dictionary RTCEncodedAudioFrameMetadata {
     member audioLevel // No implementation as of 2025-05