diff --git a/pc/BUILD.gn b/pc/BUILD.gn
index 402c364744..4cdefd4837 100644
--- a/pc/BUILD.gn
+++ b/pc/BUILD.gn
@@ -751,6 +751,8 @@ rtc_library("dtmf_sender") {
     "../rtc_base:checks",
     "../rtc_base:rtc_base",
     "../rtc_base:threading",
+    "../rtc_base/task_utils:pending_task_safety_flag",
+    "../rtc_base/task_utils:to_queued_task",
     "../rtc_base/third_party/sigslot",
   ]
   absl_deps = [
diff --git a/pc/dtmf_sender.cc b/pc/dtmf_sender.cc
index 10378028c8..5af05c8964 100644
--- a/pc/dtmf_sender.cc
+++ b/pc/dtmf_sender.cc
@@ -18,6 +18,7 @@
 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/ref_counted_object.h"
+#include "rtc_base/task_utils/to_queued_task.h"
 #include "rtc_base/thread.h"
 
 namespace webrtc {
@@ -86,19 +87,22 @@ DtmfSender::DtmfSender(rtc::Thread* signaling_thread,
 }
 
 DtmfSender::~DtmfSender() {
+  RTC_DCHECK_RUN_ON(signaling_thread_);
   StopSending();
 }
 
 void DtmfSender::RegisterObserver(DtmfSenderObserverInterface* observer) {
+  RTC_DCHECK_RUN_ON(signaling_thread_);
   observer_ = observer;
 }
 
 void DtmfSender::UnregisterObserver() {
+  RTC_DCHECK_RUN_ON(signaling_thread_);
   observer_ = nullptr;
 }
 
 bool DtmfSender::CanInsertDtmf() {
-  RTC_DCHECK(signaling_thread_->IsCurrent());
+  RTC_DCHECK_RUN_ON(signaling_thread_);
   if (!provider_) {
     return false;
   }
@@ -109,7 +113,7 @@ bool DtmfSender::InsertDtmf(const std::string& tones,
                             int duration,
                             int inter_tone_gap,
                             int comma_delay) {
-  RTC_DCHECK(signaling_thread_->IsCurrent());
+  RTC_DCHECK_RUN_ON(signaling_thread_);
 
   if (duration > kDtmfMaxDurationMs || duration < kDtmfMinDurationMs ||
       inter_tone_gap < kDtmfMinGapMs || comma_delay < kDtmfMinGapMs) {
@@ -132,38 +136,49 @@ bool DtmfSender::InsertDtmf(const std::string& tones,
   duration_ = duration;
   inter_tone_gap_ = inter_tone_gap;
   comma_delay_ = comma_delay;
-  // Clear the previous queue.
-  dtmf_driver_.Clear();
-  // Kick off a new DTMF task queue.
+
+  // Cancel any remaining tasks for previous tones.
+  if (safety_flag_) {
+    safety_flag_->SetNotAlive();
+  }
+  safety_flag_ = PendingTaskSafetyFlag::Create();
+  // Kick off a new DTMF task.
   QueueInsertDtmf(RTC_FROM_HERE, 1 /*ms*/);
   return true;
 }
 
 std::string DtmfSender::tones() const {
+  RTC_DCHECK_RUN_ON(signaling_thread_);
   return tones_;
 }
 
 int DtmfSender::duration() const {
+  RTC_DCHECK_RUN_ON(signaling_thread_);
   return duration_;
 }
 
 int DtmfSender::inter_tone_gap() const {
+  RTC_DCHECK_RUN_ON(signaling_thread_);
   return inter_tone_gap_;
 }
 
 int DtmfSender::comma_delay() const {
+  RTC_DCHECK_RUN_ON(signaling_thread_);
   return comma_delay_;
 }
 
 void DtmfSender::QueueInsertDtmf(const rtc::Location& posted_from,
                                  uint32_t delay_ms) {
-  dtmf_driver_.AsyncInvokeDelayed<void>(
-      posted_from, signaling_thread_, [this] { DoInsertDtmf(); }, delay_ms);
+  signaling_thread_->PostDelayedTask(
+      ToQueuedTask(safety_flag_,
+                   [this] {
+                     RTC_DCHECK_RUN_ON(signaling_thread_);
+                     DoInsertDtmf();
+                   }),
+      delay_ms);
 }
 
 void DtmfSender::DoInsertDtmf() {
-  RTC_DCHECK(signaling_thread_->IsCurrent());
-
   // Get the first DTMF tone from the tone buffer. Unrecognized characters will
   // be ignored and skipped.
   size_t first_tone_pos = tones_.find_first_of(kDtmfValidTones);
@@ -222,13 +237,17 @@ void DtmfSender::DoInsertDtmf() {
 }
 
 void DtmfSender::OnProviderDestroyed() {
+  RTC_DCHECK_RUN_ON(signaling_thread_);
+
   RTC_LOG(LS_INFO) << "The Dtmf provider is deleted. Clear the sending queue.";
   StopSending();
   provider_ = nullptr;
 }
 
 void DtmfSender::StopSending() {
-  dtmf_driver_.Clear();
+  if (safety_flag_) {
+    safety_flag_->SetNotAlive();
+  }
 }
 
 }  // namespace webrtc
diff --git a/pc/dtmf_sender.h b/pc/dtmf_sender.h
index 46145e5f3c..5cf7b2eba1 100644
--- a/pc/dtmf_sender.h
+++ b/pc/dtmf_sender.h
@@ -18,10 +18,10 @@
 #include "api/dtmf_sender_interface.h"
 #include "api/proxy.h"
 #include "api/scoped_refptr.h"
-#include "rtc_base/async_invoker.h"
 #include "rtc_base/constructor_magic.h"
 #include "rtc_base/location.h"
 #include "rtc_base/ref_count.h"
+#include "rtc_base/task_utils/pending_task_safety_flag.h"
 #include "rtc_base/third_party/sigslot/sigslot.h"
 #include "rtc_base/thread.h"
 
@@ -75,25 +75,27 @@ class DtmfSender : public DtmfSenderInterface, public sigslot::has_slots<> {
  private:
   DtmfSender();
 
-  void QueueInsertDtmf(const rtc::Location& posted_from, uint32_t delay_ms);
+  void QueueInsertDtmf(const rtc::Location& posted_from, uint32_t delay_ms)
+      RTC_RUN_ON(signaling_thread_);
 
   // The DTMF sending task.
-  void DoInsertDtmf();
+  void DoInsertDtmf() RTC_RUN_ON(signaling_thread_);
 
   void OnProviderDestroyed();
 
-  void StopSending();
+  void StopSending() RTC_RUN_ON(signaling_thread_);
 
-  DtmfSenderObserverInterface* observer_;
+  DtmfSenderObserverInterface* observer_ RTC_GUARDED_BY(signaling_thread_);
   rtc::Thread* signaling_thread_;
-  DtmfProviderInterface* provider_;
-  std::string tones_;
-  int duration_;
-  int inter_tone_gap_;
-  int comma_delay_;
-  // Invoker for running delayed tasks which feed the DTMF provider one tone at
-  // a time.
-  rtc::AsyncInvoker dtmf_driver_;
+  DtmfProviderInterface* provider_ RTC_GUARDED_BY(signaling_thread_);
+  std::string tones_ RTC_GUARDED_BY(signaling_thread_);
+  int duration_ RTC_GUARDED_BY(signaling_thread_);
+  int inter_tone_gap_ RTC_GUARDED_BY(signaling_thread_);
+  int comma_delay_ RTC_GUARDED_BY(signaling_thread_);
+
+  // For cancelling the tasks which feed the DTMF provider one tone at a time.
+  rtc::scoped_refptr<PendingTaskSafetyFlag> safety_flag_ RTC_GUARDED_BY(
+      signaling_thread_) RTC_PT_GUARDED_BY(signaling_thread_) = nullptr;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(DtmfSender);
 };