diff --git a/dom/media/systemservices/video_engine/desktop_capture_impl.cc b/dom/media/systemservices/video_engine/desktop_capture_impl.cc
index 6797c0eda2ef..6ea0cb2c373d 100644
--- a/dom/media/systemservices/video_engine/desktop_capture_impl.cc
+++ b/dom/media/systemservices/video_engine/desktop_capture_impl.cc
@@ -526,7 +526,7 @@ bool DesktopCaptureImpl::SetApplyRotation(bool aEnable) { return true; }
 
 int32_t DesktopCaptureImpl::StartCapture(
     const VideoCaptureCapability& aCapability) {
-  MOZ_DIAGNOSTIC_ASSERT(mControlThread->IsOnCurrentThread());
+  RTC_DCHECK_RUN_ON(&mControlThreadChecker);
 
   if (mRequestedCapability) {
     // Already initialized
@@ -558,7 +558,7 @@ int32_t DesktopCaptureImpl::StartCapture(
 }
 
 bool DesktopCaptureImpl::FocusOnSelectedSource() {
-  MOZ_DIAGNOSTIC_ASSERT(mControlThread->IsOnCurrentThread());
+  RTC_DCHECK_RUN_ON(&mControlThreadChecker);
   if (!mCaptureThread) {
     MOZ_ASSERT_UNREACHABLE(
         "FocusOnSelectedSource must be called after StartCapture");
@@ -568,6 +568,7 @@ bool DesktopCaptureImpl::FocusOnSelectedSource() {
   bool success = false;
   MOZ_ALWAYS_SUCCEEDS(mozilla::SyncRunnable::DispatchToThread(
       mCaptureThread, NS_NewRunnableFunction(__func__, [&] {
+        RTC_DCHECK_RUN_ON(&mCaptureThreadChecker);
         MOZ_ASSERT(mCapturer);
         success = mCapturer && mCapturer->FocusOnSelectedSource();
       })));
@@ -575,7 +576,7 @@ bool DesktopCaptureImpl::FocusOnSelectedSource() {
 }
 
 int32_t DesktopCaptureImpl::StopCapture() {
-  MOZ_DIAGNOSTIC_ASSERT(mControlThread->IsOnCurrentThread());
+  RTC_DCHECK_RUN_ON(&mControlThreadChecker);
   if (mRequestedCapability) {
     // Sync-cancel the capture timer so no CaptureFrame calls will come in after
     // we return.
@@ -608,7 +609,7 @@ int32_t DesktopCaptureImpl::CaptureSettings(VideoCaptureCapability& aSettings) {
 
 void DesktopCaptureImpl::OnCaptureResult(DesktopCapturer::Result aResult,
                                          std::unique_ptr<DesktopFrame> aFrame) {
-  MOZ_ASSERT(mCaptureThreadChecker.IsCurrent());
+  RTC_DCHECK_RUN_ON(&mCaptureThreadChecker);
   if (!aFrame) {
     return;
   }
@@ -693,7 +694,7 @@ void DesktopCaptureImpl::OnCaptureResult(DesktopCapturer::Result aResult,
 }
 
 void DesktopCaptureImpl::NotifyOnFrame(const VideoFrame& aFrame) {
-  MOZ_ASSERT(mCaptureThreadChecker.IsCurrent());
+  RTC_DCHECK_RUN_ON(&mCaptureThreadChecker);
   MOZ_ASSERT(Timestamp::Millis(aFrame.render_time_ms()) >
              mNextFrameMinimumTime);
   // Set the next frame's minimum time to ensure two consecutive frames don't
@@ -708,7 +709,7 @@ void DesktopCaptureImpl::NotifyOnFrame(const VideoFrame& aFrame) {
 
 void DesktopCaptureImpl::InitOnThread(
     std::unique_ptr<DesktopCapturer> aCapturer, int aFramerate) {
-  MOZ_DIAGNOSTIC_ASSERT(mCaptureThreadChecker.IsCurrent());
+  RTC_DCHECK_RUN_ON(&mCaptureThreadChecker);
 
   mCapturer = std::move(aCapturer);
 
@@ -723,7 +724,7 @@ void DesktopCaptureImpl::InitOnThread(
 }
 
 void DesktopCaptureImpl::ShutdownOnThread() {
-  MOZ_DIAGNOSTIC_ASSERT(mCaptureThreadChecker.IsCurrent());
+  RTC_DCHECK_RUN_ON(&mCaptureThreadChecker);
   if (mCaptureTimer) {
     mCaptureTimer->Cancel();
     mCaptureTimer = nullptr;
@@ -737,7 +738,7 @@ void DesktopCaptureImpl::ShutdownOnThread() {
 }
 
 void DesktopCaptureImpl::CaptureFrameOnThread() {
-  MOZ_DIAGNOSTIC_ASSERT(mCaptureThreadChecker.IsCurrent());
+  RTC_DCHECK_RUN_ON(&mCaptureThreadChecker);
 
 #if defined(WEBRTC_MAC)
   // Give cycles to the RunLoop so frame callbacks can happen
diff --git a/dom/media/systemservices/video_engine/desktop_capture_impl.h b/dom/media/systemservices/video_engine/desktop_capture_impl.h
index 5773bf1ac398..64eadb140131 100644
--- a/dom/media/systemservices/video_engine/desktop_capture_impl.h
+++ b/dom/media/systemservices/video_engine/desktop_capture_impl.h
@@ -215,23 +215,27 @@ class DesktopCaptureImpl : public DesktopCapturer::Callback,
   // Control thread on which the public API is called.
   const nsCOMPtr<nsISerialEventTarget> mControlThread;
   // Set in StartCapture.
-  mozilla::Maybe<VideoCaptureCapability> mRequestedCapability;
+  mozilla::Maybe<VideoCaptureCapability> mRequestedCapability
+      RTC_GUARDED_BY(mControlThreadChecker);
   // The DesktopCapturer is created on mControlThread but assigned and accessed
   // only on mCaptureThread.
-  std::unique_ptr<DesktopCapturer> mCapturer;
-  // Dedicated thread that does the capturing. Only used on mControlThread.
-  nsCOMPtr<nsIThread> mCaptureThread;
+  std::unique_ptr<DesktopCapturer> mCapturer
+      RTC_GUARDED_BY(mCaptureThreadChecker);
+  // Dedicated thread that does the capturing.
+  nsCOMPtr<nsIThread> mCaptureThread RTC_GUARDED_BY(mControlThreadChecker);
+  // Checks that API methods are called on mControlThread.
+  webrtc::SequenceChecker mControlThreadChecker;
   // Checks that frame delivery only happens on mCaptureThread.
   webrtc::SequenceChecker mCaptureThreadChecker;
   // Timer that triggers frame captures. Only used on mCaptureThread.
   // TODO(Bug 1806646): Drive capture with vsync instead.
-  nsCOMPtr<nsITimer> mCaptureTimer;
+  nsCOMPtr<nsITimer> mCaptureTimer RTC_GUARDED_BY(mCaptureThreadChecker);
   // Interval between captured frames, based on the framerate in
   // mRequestedCapability. mCaptureThread only.
-  mozilla::Maybe<mozilla::TimeDuration> mRequestedCaptureInterval;
+  mozilla::Maybe<mozilla::TimeDuration> mRequestedCaptureInterval
+      RTC_GUARDED_BY(mCaptureThreadChecker);
   // Used to make sure incoming timestamp is increasing for every frame.
-  // mCaptureThread only.
-  webrtc::Timestamp mNextFrameMinimumTime;
+  webrtc::Timestamp mNextFrameMinimumTime RTC_GUARDED_BY(mCaptureThreadChecker);
   // Callbacks for captured frames. Mutated on mControlThread, callbacks happen
   // on mCaptureThread.
   mozilla::DataMutex<std::set<rtc::VideoSinkInterface<VideoFrame>*>> mCallbacks;