diff --git a/pc/peerconnection.cc b/pc/peerconnection.cc
index da34cc2935..642ff49bb9 100644
--- a/pc/peerconnection.cc
+++ b/pc/peerconnection.cc
@@ -6156,6 +6156,10 @@ bool PeerConnection::HasRtcpMuxEnabled(const cricket::ContentInfo* content) {
 static RTCError ValidateMids(const cricket::SessionDescription& description) {
   std::set<std::string> mids;
   for (const cricket::ContentInfo& content : description.contents()) {
+    if (content.name.empty()) {
+      LOG_AND_RETURN_ERROR(RTCErrorType::INVALID_PARAMETER,
+                           "A media section is missing a MID attribute.");
+    }
     if (!mids.insert(content.name).second) {
       LOG_AND_RETURN_ERROR(RTCErrorType::INVALID_PARAMETER,
                            "Duplicate a=mid value '" + content.name + "'.");
diff --git a/pc/peerconnection_jsep_unittest.cc b/pc/peerconnection_jsep_unittest.cc
index b8606646d3..7a04474787 100644
--- a/pc/peerconnection_jsep_unittest.cc
+++ b/pc/peerconnection_jsep_unittest.cc
@@ -1694,4 +1694,20 @@ TEST_F(PeerConnectionJsepTest, LegacyNoMidAudioVideoAnswer) {
   ASSERT_TRUE(caller->SetRemoteDescription(std::move(answer)));
 }
 
+// Test that SetLocalDescription fails if a=mid lines are missing.
+TEST_F(PeerConnectionJsepTest, SetLocalDescriptionFailsMissingMid) {
+  auto caller = CreatePeerConnection();
+  caller->AddAudioTrack("audio");
+
+  auto offer = caller->CreateOffer();
+  ClearMids(offer.get());
+
+  std::string error;
+  ASSERT_FALSE(caller->SetLocalDescription(std::move(offer), &error));
+  EXPECT_EQ(
+      "Failed to set local offer sdp: A media section is missing a MID "
+      "attribute.",
+      error);
+}
+
 }  // namespace webrtc