diff --git a/dom/media/tests/mochitest/sdpUtils.js b/dom/media/tests/mochitest/sdpUtils.js
index 17f23f9c924e..a27c2e308f61 100644
--- a/dom/media/tests/mochitest/sdpUtils.js
+++ b/dom/media/tests/mochitest/sdpUtils.js
@@ -238,6 +238,10 @@ var sdputils = {
       .replace(
         /a=extmap:[^\s]* urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id.*\r\n/g,
         ""
+      )
+      .replace(
+        /a=extmap:[^\s]* urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id.*\r\n/g,
+        ""
       );
   },
 
@@ -265,6 +269,16 @@ var sdputils = {
       "a=extmap:" +
       extmap_id[1] +
       "/recvonly urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id\r\n";
+    var extmap_id = offer_sdp.match(
+      "a=extmap:([0-9+])/sendonly urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id"
+    );
+    ok(extmap_id != null, "Offer contains RID RTP header extension");
+    new_answer_sdp =
+      new_answer_sdp +
+      "a=extmap:" +
+      extmap_id[1] +
+      "/recvonly urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id\r\n";
+
     return new_answer_sdp;
   },