diff --git a/pc/peer_connection_simulcast_unittest.cc b/pc/peer_connection_simulcast_unittest.cc
index e704aeba5a..b9681dca34 100644
--- a/pc/peer_connection_simulcast_unittest.cc
+++ b/pc/peer_connection_simulcast_unittest.cc
@@ -602,6 +602,27 @@ TEST_F(PeerConnectionSimulcastTests, SimulcastAudioRejected) {
               ElementsAre(Field("rid", &RtpEncodingParameters::rid, Eq(""))));
 }
 
+// Check that modifying the offer to remove simulcast and at the same
+// time leaving in a RID line does not cause an exception.
+TEST_F(PeerConnectionSimulcastTests, SimulcastSldModificationRejected) {
+  auto local = CreatePeerConnectionWrapper();
+  auto remote = CreatePeerConnectionWrapper();
+  auto layers = CreateLayers({"1", "2", "3"}, true);
+  AddTransceiver(local.get(), layers);
+  auto offer = local->CreateOffer();
+  std::string as_string;
+  EXPECT_TRUE(offer->ToString(&as_string));
+  auto simulcast_marker = "a=rid:3 send\r\na=simulcast:send 1;2;3\r\n";
+  auto pos = as_string.find(simulcast_marker);
+  EXPECT_NE(pos, std::string::npos);
+  as_string.erase(pos, strlen(simulcast_marker));
+  SdpParseError parse_error;
+  auto modified_offer =
+      CreateSessionDescription(SdpType::kOffer, as_string, &parse_error);
+  EXPECT_TRUE(modified_offer);
+  EXPECT_TRUE(local->SetLocalDescription(std::move(modified_offer)));
+}
+
 #if RTC_METRICS_ENABLED
 //
 // Checks the logged metrics when simulcast is not used.
diff --git a/pc/webrtc_sdp.cc b/pc/webrtc_sdp.cc
index 8e4552476b..c942689b8f 100644
--- a/pc/webrtc_sdp.cc
+++ b/pc/webrtc_sdp.cc
@@ -3282,7 +3282,6 @@ bool ParseContent(absl::string_view message,
 
   // If simulcast is specifed, split the rids into send and receive.
   // Rids that do not appear in simulcast attribute will be removed.
-  // If it is not specified, we assume that all rids are for send layers.
   std::vector<RidDescription> send_rids;
   std::vector<RidDescription> receive_rids;
   if (!simulcast.empty()) {
@@ -3309,7 +3308,11 @@ bool ParseContent(absl::string_view message,
 
     media_desc->set_simulcast_description(simulcast);
   } else {
-    send_rids = rids;
+    // RID is specified in RFC 8851, which identifies a lot of usages.
+    // We only support RFC 8853 usage of RID, not anything else.
+    // Ignore all RID parameters when a=simulcast is missing.
+    // In particular do NOT do send_rids = rids;
+    RTC_LOG(LS_VERBOSE) << "Ignoring send_rids without simulcast";
   }
 
   media_desc->set_receive_rids(receive_rids);