diff --git a/pc/jseptransportcontroller.cc b/pc/jseptransportcontroller.cc
index 31d27cae4d..b5ce5fe0a7 100644
--- a/pc/jseptransportcontroller.cc
+++ b/pc/jseptransportcontroller.cc
@@ -589,7 +589,7 @@ RTCError JsepTransportController::ApplyDescription_n(
     }
 
     std::vector<int> extension_ids;
-    if (bundle_group_ && content_info.name == *bundled_mid()) {
+    if (bundled_mid() && content_info.name == *bundled_mid()) {
       extension_ids = merged_encrypted_extension_ids;
     } else {
       extension_ids = GetEncryptedHeaderExtensionIds(content_info);
@@ -685,8 +685,9 @@ RTCError JsepTransportController::ValidateAndMaybeUpdateBundleGroup(
   }
 
   if (ShouldUpdateBundleGroup(type, description)) {
-    std::string new_bundled_mid = *(new_bundle_group->FirstContentName());
-    if (bundled_mid() && *bundled_mid() != new_bundled_mid) {
+    const std::string* new_bundled_mid = new_bundle_group->FirstContentName();
+    if (bundled_mid() && new_bundled_mid &&
+        *bundled_mid() != *new_bundled_mid) {
       return RTCError(RTCErrorType::UNSUPPORTED_OPERATION,
                       "Changing the negotiated BUNDLE-tag is not supported.");
     }
diff --git a/pc/jseptransportcontroller.h b/pc/jseptransportcontroller.h
index 794175a6e2..6e44534f08 100644
--- a/pc/jseptransportcontroller.h
+++ b/pc/jseptransportcontroller.h
@@ -201,8 +201,8 @@ class JsepTransportController : public sigslot::has_slots<>,
 
   rtc::Optional<std::string> bundled_mid() const {
     rtc::Optional<std::string> bundled_mid;
-    if (bundle_group_) {
-      bundled_mid = std::move(*(bundle_group_->FirstContentName()));
+    if (bundle_group_ && bundle_group_->FirstContentName()) {
+      bundled_mid = *(bundle_group_->FirstContentName());
     }
     return bundled_mid;
   }
diff --git a/pc/mediasession.cc b/pc/mediasession.cc
index 3bf931c613..eba3249d03 100644
--- a/pc/mediasession.cc
+++ b/pc/mediasession.cc
@@ -1494,10 +1494,17 @@ SessionDescription* MediaSessionDescriptionFactory::CreateAnswer(
     }
   }
 
-  // Only put BUNDLE group in answer if nonempty.
-  if (answer_bundle.FirstContentName()) {
+  // If a BUNDLE group was offered, put a BUNDLE group in the answer even if
+  // it's empty. RFC5888 says:
+  //
+  //   A SIP entity that receives an offer that contains an "a=group" line
+  //   with semantics that are understood MUST return an answer that
+  //   contains an "a=group" line with the same semantics.
+  if (offer_bundle) {
     answer->AddGroup(answer_bundle);
+  }
 
+  if (answer_bundle.FirstContentName()) {
     // Share the same ICE credentials and crypto params across all contents,
     // as BUNDLE requires.
     if (!UpdateTransportInfoForBundle(answer_bundle, answer.get())) {
diff --git a/pc/peerconnection_bundle_unittest.cc b/pc/peerconnection_bundle_unittest.cc
index c71662bda0..a1b69d8ae1 100644
--- a/pc/peerconnection_bundle_unittest.cc
+++ b/pc/peerconnection_bundle_unittest.cc
@@ -248,6 +248,13 @@ class PeerConnectionBundleTest
   PeerConnectionBundleTest() : PeerConnectionBundleBaseTest(GetParam()) {}
 };
 
+class PeerConnectionBundleTestUnifiedPlan
+    : public PeerConnectionBundleBaseTest {
+ protected:
+  PeerConnectionBundleTestUnifiedPlan()
+      : PeerConnectionBundleBaseTest(SdpSemantics::kUnifiedPlan) {}
+};
+
 SdpContentMutator RemoveRtcpMux() {
   return [](cricket::ContentInfo* content, cricket::TransportInfo* transport) {
     content->media_description()->set_rtcp_mux(false);
@@ -804,4 +811,34 @@ INSTANTIATE_TEST_CASE_P(PeerConnectionBundleTest,
                         Values(SdpSemantics::kPlanB,
                                SdpSemantics::kUnifiedPlan));
 
+// According to RFC5888, if an endpoint understands the semantics of an
+// "a=group", it MUST return an answer with that group. So, an empty BUNDLE
+// group is valid when the answerer rejects all m= sections (by stopping all
+// transceivers), meaning there's nothing to bundle.
+//
+// Only writing this test for Unified Plan mode, since there's no way to reject
+// m= sections in answers for Plan B without SDP munging.
+TEST_F(PeerConnectionBundleTestUnifiedPlan,
+       EmptyBundleGroupCreatedInAnswerWhenAppropriate) {
+  auto caller = CreatePeerConnectionWithAudioVideo();
+  auto callee = CreatePeerConnection();
+
+  EXPECT_TRUE(callee->SetRemoteDescription(caller->CreateOfferAndSetAsLocal()));
+
+  // Stop all transceivers, causing all m= sections to be rejected.
+  for (const auto& transceiver : callee->pc()->GetTransceivers()) {
+    transceiver->Stop();
+  }
+  EXPECT_TRUE(
+      caller->SetRemoteDescription(callee->CreateAnswerAndSetAsLocal()));
+
+  // Verify that the answer actually contained an empty bundle group.
+  const SessionDescriptionInterface* desc = callee->pc()->local_description();
+  ASSERT_NE(nullptr, desc);
+  const cricket::ContentGroup* bundle_group =
+      desc->description()->GetGroupByName(cricket::GROUP_TYPE_BUNDLE);
+  ASSERT_NE(nullptr, bundle_group);
+  EXPECT_TRUE(bundle_group->content_names().empty());
+}
+
 }  // namespace webrtc