diff --git a/sdk/objc/api/peerconnection/RTCConfiguration.h b/sdk/objc/api/peerconnection/RTCConfiguration.h
index 59d3572f27..af42c4522c 100644
--- a/sdk/objc/api/peerconnection/RTCConfiguration.h
+++ b/sdk/objc/api/peerconnection/RTCConfiguration.h
@@ -227,6 +227,12 @@ RTC_OBJC_EXPORT
  */
 @property(nonatomic, assign) BOOL enableImplicitRollback;
 
+/**
+ * Control if "a=extmap-allow-mixed" is included in the offer.
+ * See: https://www.chromestatus.com/feature/6269234631933952
+ */
+@property(nonatomic, assign) BOOL offerExtmapAllowMixed;
+
 - (instancetype)init;
 
 @end
diff --git a/sdk/objc/api/peerconnection/RTCConfiguration.mm b/sdk/objc/api/peerconnection/RTCConfiguration.mm
index 5164a3c969..d003eed1e3 100644
--- a/sdk/objc/api/peerconnection/RTCConfiguration.mm
+++ b/sdk/objc/api/peerconnection/RTCConfiguration.mm
@@ -57,6 +57,7 @@
 @synthesize rtcpAudioReportIntervalMs = _rtcpAudioReportIntervalMs;
 @synthesize rtcpVideoReportIntervalMs = _rtcpVideoReportIntervalMs;
 @synthesize enableImplicitRollback = _enableImplicitRollback;
+@synthesize offerExtmapAllowMixed = _offerExtmapAllowMixed;
 
 - (instancetype)init {
   // Copy defaults.
@@ -136,6 +137,7 @@
     _rtcpVideoReportIntervalMs = config.video_rtcp_report_interval_ms();
     _allowCodecSwitching = config.allow_codec_switching.value_or(false);
     _enableImplicitRollback = config.enable_implicit_rollback;
+    _offerExtmapAllowMixed = config.offer_extmap_allow_mixed;
   }
   return self;
 }
@@ -268,6 +270,7 @@
   nativeConfig->set_video_rtcp_report_interval_ms(_rtcpVideoReportIntervalMs);
   nativeConfig->allow_codec_switching = _allowCodecSwitching;
   nativeConfig->enable_implicit_rollback = _enableImplicitRollback;
+  nativeConfig->offer_extmap_allow_mixed = _offerExtmapAllowMixed;
   return nativeConfig.release();
 }