diff --git a/src/handlers/sdp/MediaSection.ts b/src/handlers/sdp/MediaSection.ts
index c619f5de..a0a57616 100644
--- a/src/handlers/sdp/MediaSection.ts
+++ b/src/handlers/sdp/MediaSection.ts
@@ -338,6 +338,31 @@ export class AnswerMediaSection extends MediaSection {
 					});
 				}
 
+				// Starting with Chrome 148, libwebrtc records every extmap ID seen in
+				// a local offer into a per-PeerConnection history
+				// (historical_rtp_header_extensions_ in BaseChannel, introduced in
+				// https://webrtc.googlesource.com/src/+/5788235). Any subsequent
+				// setLocalDescription that tries to bind the same ID to a different
+				// URI is rejected with "RTP extension ID reassignment not supported".
+				//
+				// Previously, extensions unsupported by the server were simply omitted
+				// from the synthetic answer. Chrome then considered their IDs "free"
+				// and could reuse them when negotiating new m-sections (e.g. adding
+				// audio after video simulcast), triggering the reassignment error.
+				// Including them back in the answer — even without server support —
+				// causes Chrome to permanently associate those IDs with their original
+				// URIs, preventing any future reuse.
+				const confirmedExtUris = new Set(this._mediaObject.ext.map(e => e.uri));
+
+				for (const offerExt of offerMediaObject.ext ?? []) {
+					if (!confirmedExtUris.has(offerExt.uri)) {
+						this._mediaObject.ext.push({
+							uri: offerExt.uri,
+							value: offerExt.value,
+						});
+					}
+				}
+
 				// Allow both 1 byte and 2 bytes length header extensions since
 				// mediasoup can receive both at any time.
 				if (offerMediaObject.extmapAllowMixed === 'extmap-allow-mixed') {
diff --git a/src/handlers/sdp/RemoteSdp.ts b/src/handlers/sdp/RemoteSdp.ts
index 31b91544..2c09c85d 100644
--- a/src/handlers/sdp/RemoteSdp.ts
+++ b/src/handlers/sdp/RemoteSdp.ts
@@ -18,8 +18,6 @@ import type { MediaKind, RtpParameters } from '../../RtpParameters';
 import type { SctpParameters } from '../../SctpParameters';
 import { version as mediasoupClientVersion } from '../../';
 
-const DependencyDescriptorCodecs = ['av1', 'h264'];
-
 const logger = new Logger('RemoteSdp');
 
 export class RemoteSdp {
@@ -175,22 +173,6 @@ export class RemoteSdp {
 			codecOptions,
 		});
 
-		const mediaObject = mediaSection.getObject();
-
-		// Remove Dependency Descriptor extension unless there is support for
-		// the codec in mediasoup.
-		const ddCodec = mediaObject.rtp.find(rtp =>
-			DependencyDescriptorCodecs.includes(rtp.codec.toLowerCase())
-		);
-
-		if (!ddCodec) {
-			mediaObject.ext = mediaObject.ext?.filter(
-				extmap =>
-					extmap.uri !==
-					'https://aomediacodec.github.io/av1-rtp-spec/#dependency-descriptor-rtp-header-extension'
-			);
-		}
-
 		// Unified-Plan with closed media section replacement.
 		if (reuseMid) {
 			this.replaceMediaSection(mediaSection, reuseMid);