diff --git a/webrtc/modules/rtp_rtcp/include/flexfec_sender.h b/webrtc/modules/rtp_rtcp/include/flexfec_sender.h
index 48d3da02ac..fa4bd6e7ec 100644
--- a/webrtc/modules/rtp_rtcp/include/flexfec_sender.h
+++ b/webrtc/modules/rtp_rtcp/include/flexfec_sender.h
@@ -29,6 +29,9 @@ namespace webrtc {
 
 class RtpPacketToSend;
 
+// Note that this class is not thread safe, and thus requires external
+// synchronization.
+
 class FlexfecSender {
  public:
   FlexfecSender(int payload_type,
@@ -62,9 +65,8 @@ class FlexfecSender {
  private:
   // Utility.
   Clock* const clock_;
-  Random random_ GUARDED_BY(sequence_checker_);
-  int64_t last_generated_packet_ms_ GUARDED_BY(sequence_checker_);
-  rtc::SequencedTaskChecker sequence_checker_;
+  Random random_;
+  int64_t last_generated_packet_ms_;
 
   // Config.
   const int payload_type_;
@@ -72,10 +74,10 @@ class FlexfecSender {
   const uint32_t ssrc_;
   const uint32_t protected_media_ssrc_;
   // Sequence number of next packet to generate.
-  uint16_t seq_num_ GUARDED_BY(sequence_checker_);
+  uint16_t seq_num_;
 
   // Implementation.
-  UlpfecGenerator ulpfec_generator_ GUARDED_BY(sequence_checker_);
+  UlpfecGenerator ulpfec_generator_;
   const RtpHeaderExtensionMap rtp_header_extension_map_;
 };
 
diff --git a/webrtc/modules/rtp_rtcp/source/flexfec_sender.cc b/webrtc/modules/rtp_rtcp/source/flexfec_sender.cc
index ec8bbdcbe9..5019456841 100644
--- a/webrtc/modules/rtp_rtcp/source/flexfec_sender.cc
+++ b/webrtc/modules/rtp_rtcp/source/flexfec_sender.cc
@@ -80,10 +80,6 @@ FlexfecSender::FlexfecSender(
   // This object should not have been instantiated if FlexFEC is disabled.
   RTC_DCHECK_GE(payload_type, 0);
   RTC_DCHECK_LE(payload_type, 127);
-
-  // It's OK to create this object on a different thread/task queue than
-  // the one used during main operation.
-  sequence_checker_.Detach();
 }
 
 FlexfecSender::~FlexfecSender() = default;
@@ -91,13 +87,10 @@ FlexfecSender::~FlexfecSender() = default;
 // We are reusing the implementation from UlpfecGenerator for SetFecParameters,
 // AddRtpPacketAndGenerateFec, and FecAvailable.
 void FlexfecSender::SetFecParameters(const FecProtectionParams& params) {
-  RTC_DCHECK_CALLED_SEQUENTIALLY(&sequence_checker_);
   ulpfec_generator_.SetFecParameters(params);
 }
 
-bool FlexfecSender::AddRtpPacketAndGenerateFec(
-    const RtpPacketToSend& packet) {
-  RTC_DCHECK_CALLED_SEQUENTIALLY(&sequence_checker_);
+bool FlexfecSender::AddRtpPacketAndGenerateFec(const RtpPacketToSend& packet) {
   // TODO(brandtr): Generalize this SSRC check when we support multistream
   // protection.
   RTC_DCHECK_EQ(packet.Ssrc(), protected_media_ssrc_);
@@ -106,14 +99,10 @@ bool FlexfecSender::AddRtpPacketAndGenerateFec(
 }
 
 bool FlexfecSender::FecAvailable() const {
-  RTC_DCHECK_CALLED_SEQUENTIALLY(&sequence_checker_);
   return ulpfec_generator_.FecAvailable();
 }
 
-std::vector<std::unique_ptr<RtpPacketToSend>>
-FlexfecSender::GetFecPackets() {
-  RTC_DCHECK_CALLED_SEQUENTIALLY(&sequence_checker_);
-
+std::vector<std::unique_ptr<RtpPacketToSend>> FlexfecSender::GetFecPackets() {
   std::vector<std::unique_ptr<RtpPacketToSend>> fec_packets_to_send;
   fec_packets_to_send.reserve(ulpfec_generator_.generated_fec_packets_.size());
   for (const auto& fec_packet : ulpfec_generator_.generated_fec_packets_) {