diff --git a/test/time_controller/BUILD.gn b/test/time_controller/BUILD.gn
index c3d5dc9..ac396b9 100644
--- a/test/time_controller/BUILD.gn
+++ b/test/time_controller/BUILD.gn
@@ -37,6 +37,7 @@
     "../../rtc_base:checks",
     "../../rtc_base:rtc_base_tests_utils",
     "../../rtc_base:rtc_event",
+    "../../rtc_base/synchronization:mutex",
     "../../rtc_base/synchronization:sequence_checker",
     "../../rtc_base/synchronization:yield_policy",
     "../../rtc_base/task_utils:to_queued_task",
diff --git a/test/time_controller/simulated_process_thread.cc b/test/time_controller/simulated_process_thread.cc
index df90f54..e001841 100644
--- a/test/time_controller/simulated_process_thread.cc
+++ b/test/time_controller/simulated_process_thread.cc
@@ -39,7 +39,7 @@
 
 void SimulatedProcessThread::RunReady(Timestamp at_time) {
   CurrentTaskQueueSetter set_current(this);
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   std::vector<Module*> ready_modules;
   for (auto it = delayed_modules_.begin();
        it != delayed_modules_.end() && it->first <= at_time;
@@ -63,10 +63,10 @@
   while (!queue_.empty()) {
     std::unique_ptr<QueuedTask> task = std::move(queue_.front());
     queue_.pop_front();
-    lock_.Leave();
+    lock_.Unlock();
     bool should_delete = task->Run();
     RTC_CHECK(should_delete);
-    lock_.Enter();
+    lock_.Lock();
   }
   RTC_DCHECK(queue_.empty());
   if (!delayed_modules_.empty()) {
@@ -81,7 +81,7 @@
 void SimulatedProcessThread::Start() {
   std::vector<Module*> starting;
   {
-    rtc::CritScope lock(&lock_);
+    MutexLock lock(&lock_);
     if (process_thread_running_)
       return;
     process_thread_running_ = true;
@@ -91,7 +91,7 @@
     module->ProcessThreadAttached(this);
 
   Timestamp at_time = handler_->CurrentTime();
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   for (auto& module : starting)
     delayed_modules_[GetNextTime(module, at_time)].push_back(module);
 
@@ -107,7 +107,7 @@
 void SimulatedProcessThread::Stop() {
   std::vector<Module*> stopping;
   {
-    rtc::CritScope lock(&lock_);
+    MutexLock lock(&lock_);
     process_thread_running_ = false;
 
     for (auto& delayed : delayed_modules_) {
@@ -123,7 +123,7 @@
 }
 
 void SimulatedProcessThread::WakeUp(Module* module) {
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   for (auto it = delayed_modules_.begin(); it != delayed_modules_.end(); ++it) {
     if (RemoveByValue(&it->second, module))
       break;
@@ -136,7 +136,7 @@
 void SimulatedProcessThread::RegisterModule(Module* module,
                                             const rtc::Location& from) {
   module->ProcessThreadAttached(this);
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   if (!process_thread_running_) {
     stopped_modules_.push_back(module);
   } else {
@@ -149,7 +149,7 @@
 void SimulatedProcessThread::DeRegisterModule(Module* module) {
   bool modules_running;
   {
-    rtc::CritScope lock(&lock_);
+    MutexLock lock(&lock_);
     if (!process_thread_running_) {
       RemoveByValue(&stopped_modules_, module);
     } else {
@@ -165,14 +165,14 @@
 }
 
 void SimulatedProcessThread::PostTask(std::unique_ptr<QueuedTask> task) {
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   queue_.emplace_back(std::move(task));
   next_run_time_ = Timestamp::MinusInfinity();
 }
 
 void SimulatedProcessThread::PostDelayedTask(std::unique_ptr<QueuedTask> task,
                                              uint32_t milliseconds) {
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   Timestamp target_time =
       handler_->CurrentTime() + TimeDelta::Millis(milliseconds);
   delayed_tasks_[target_time].push_back(std::move(task));
diff --git a/test/time_controller/simulated_process_thread.h b/test/time_controller/simulated_process_thread.h
index 6026826..54d5db7 100644
--- a/test/time_controller/simulated_process_thread.h
+++ b/test/time_controller/simulated_process_thread.h
@@ -16,6 +16,7 @@
 #include <memory>
 #include <vector>
 
+#include "rtc_base/synchronization/mutex.h"
 #include "test/time_controller/simulated_time_controller.h"
 
 namespace webrtc {
@@ -29,7 +30,7 @@
   void RunReady(Timestamp at_time) override;
 
   Timestamp GetNextRunTime() const override {
-    rtc::CritScope lock(&lock_);
+    MutexLock lock(&lock_);
     return next_run_time_;
   }
 
@@ -55,7 +56,7 @@
   sim_time_impl::SimulatedTimeControllerImpl* const handler_;
   // Using char* to be debugger friendly.
   char* name_;
-  rtc::CriticalSection lock_;
+  mutable Mutex lock_;
   Timestamp next_run_time_ RTC_GUARDED_BY(lock_) = Timestamp::PlusInfinity();
 
   std::deque<std::unique_ptr<QueuedTask>> queue_;
diff --git a/test/time_controller/simulated_task_queue.cc b/test/time_controller/simulated_task_queue.cc
index 59fabc2..da675af 100644
--- a/test/time_controller/simulated_task_queue.cc
+++ b/test/time_controller/simulated_task_queue.cc
@@ -32,7 +32,7 @@
   std::deque<std::unique_ptr<QueuedTask>> ready_tasks;
   std::map<Timestamp, std::vector<std::unique_ptr<QueuedTask>>> delayed_tasks;
   {
-    rtc::CritScope lock(&lock_);
+    MutexLock lock(&lock_);
     ready_tasks_.swap(ready_tasks);
     delayed_tasks_.swap(delayed_tasks);
   }
@@ -42,7 +42,7 @@
 }
 
 void SimulatedTaskQueue::RunReady(Timestamp at_time) {
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   for (auto it = delayed_tasks_.begin();
        it != delayed_tasks_.end() && it->first <= at_time;
        it = delayed_tasks_.erase(it)) {
@@ -54,14 +54,14 @@
   while (!ready_tasks_.empty()) {
     std::unique_ptr<QueuedTask> ready = std::move(ready_tasks_.front());
     ready_tasks_.pop_front();
-    lock_.Leave();
+    lock_.Unlock();
     bool delete_task = ready->Run();
     if (delete_task) {
       ready.reset();
     } else {
       ready.release();
     }
-    lock_.Enter();
+    lock_.Lock();
   }
   if (!delayed_tasks_.empty()) {
     next_run_time_ = delayed_tasks_.begin()->first;
@@ -71,14 +71,14 @@
 }
 
 void SimulatedTaskQueue::PostTask(std::unique_ptr<QueuedTask> task) {
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   ready_tasks_.emplace_back(std::move(task));
   next_run_time_ = Timestamp::MinusInfinity();
 }
 
 void SimulatedTaskQueue::PostDelayedTask(std::unique_ptr<QueuedTask> task,
                                          uint32_t milliseconds) {
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   Timestamp target_time =
       handler_->CurrentTime() + TimeDelta::Millis(milliseconds);
   delayed_tasks_[target_time].push_back(std::move(task));
diff --git a/test/time_controller/simulated_task_queue.h b/test/time_controller/simulated_task_queue.h
index 940117c..5035f79 100644
--- a/test/time_controller/simulated_task_queue.h
+++ b/test/time_controller/simulated_task_queue.h
@@ -15,6 +15,7 @@
 #include <memory>
 #include <vector>
 
+#include "rtc_base/synchronization/mutex.h"
 #include "test/time_controller/simulated_time_controller.h"
 
 namespace webrtc {
@@ -30,7 +31,7 @@
   void RunReady(Timestamp at_time) override;
 
   Timestamp GetNextRunTime() const override {
-    rtc::CritScope lock(&lock_);
+    MutexLock lock(&lock_);
     return next_run_time_;
   }
   TaskQueueBase* GetAsTaskQueue() override { return this; }
@@ -46,7 +47,7 @@
   // Using char* to be debugger friendly.
   char* name_;
 
-  rtc::CriticalSection lock_;
+  mutable Mutex lock_;
 
   std::deque<std::unique_ptr<QueuedTask>> ready_tasks_ RTC_GUARDED_BY(lock_);
   std::map<Timestamp, std::vector<std::unique_ptr<QueuedTask>>> delayed_tasks_
diff --git a/test/time_controller/simulated_thread.cc b/test/time_controller/simulated_thread.cc
index 8d1637c..8071264 100644
--- a/test/time_controller/simulated_thread.cc
+++ b/test/time_controller/simulated_thread.cc
@@ -59,7 +59,7 @@
   CurrentThreadSetter set_current(this);
   ProcessMessages(0);
   int delay_ms = GetDelay();
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   if (delay_ms == kForever) {
     next_run_time_ = Timestamp::PlusInfinity();
   } else {
@@ -95,7 +95,7 @@
                            rtc::MessageData* pdata,
                            bool time_sensitive) {
   rtc::Thread::Post(posted_from, phandler, id, pdata, time_sensitive);
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   next_run_time_ = Timestamp::MinusInfinity();
 }
 
@@ -105,7 +105,7 @@
                                   uint32_t id,
                                   rtc::MessageData* pdata) {
   rtc::Thread::PostDelayed(posted_from, delay_ms, phandler, id, pdata);
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   next_run_time_ =
       std::min(next_run_time_, Timestamp::Millis(rtc::TimeMillis() + delay_ms));
 }
@@ -116,7 +116,7 @@
                              uint32_t id,
                              rtc::MessageData* pdata) {
   rtc::Thread::PostAt(posted_from, target_time_ms, phandler, id, pdata);
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   next_run_time_ = std::min(next_run_time_, Timestamp::Millis(target_time_ms));
 }
 
diff --git a/test/time_controller/simulated_thread.h b/test/time_controller/simulated_thread.h
index fd39696..b6c1e6e 100644
--- a/test/time_controller/simulated_thread.h
+++ b/test/time_controller/simulated_thread.h
@@ -12,6 +12,7 @@
 
 #include <memory>
 
+#include "rtc_base/synchronization/mutex.h"
 #include "test/time_controller/simulated_time_controller.h"
 
 namespace webrtc {
@@ -28,7 +29,7 @@
   void RunReady(Timestamp at_time) override;
 
   Timestamp GetNextRunTime() const override {
-    rtc::CritScope lock(&lock_);
+    MutexLock lock(&lock_);
     return next_run_time_;
   }
 
@@ -61,7 +62,7 @@
   sim_time_impl::SimulatedTimeControllerImpl* const handler_;
   // Using char* to be debugger friendly.
   char* name_;
-  rtc::CriticalSection lock_;
+  mutable Mutex lock_;
   Timestamp next_run_time_ RTC_GUARDED_BY(lock_) = Timestamp::PlusInfinity();
 };
 
diff --git a/test/time_controller/simulated_time_controller.cc b/test/time_controller/simulated_time_controller.cc
index 769be3f..aba8c66 100644
--- a/test/time_controller/simulated_time_controller.cc
+++ b/test/time_controller/simulated_time_controller.cc
@@ -95,7 +95,7 @@
   // Using a dummy thread rather than nullptr to avoid implicit thread creation
   // by Thread::Current().
   SimulatedThread::CurrentThreadSetter set_current(dummy_thread_.get());
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   RTC_DCHECK_EQ(rtc::CurrentThreadId(), thread_id_);
   Timestamp current_time = CurrentTime();
   // Clearing |ready_runners_| in case this is a recursive call:
@@ -116,25 +116,25 @@
     while (!ready_runners_.empty()) {
       auto* runner = ready_runners_.front();
       ready_runners_.pop_front();
-      lock_.Leave();
+      lock_.Unlock();
       // Note that the RunReady function might indirectly cause a call to
       // Unregister() which will grab |lock_| again to remove items from
       // |ready_runners_|.
       runner->RunReady(current_time);
-      lock_.Enter();
+      lock_.Lock();
     }
   }
 }
 
 Timestamp SimulatedTimeControllerImpl::CurrentTime() const {
-  rtc::CritScope lock(&time_lock_);
+  MutexLock lock(&time_lock_);
   return current_time_;
 }
 
 Timestamp SimulatedTimeControllerImpl::NextRunTime() const {
   Timestamp current_time = CurrentTime();
   Timestamp next_time = Timestamp::PlusInfinity();
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   for (auto* runner : runners_) {
     Timestamp next_run_time = runner->GetNextRunTime();
     if (next_run_time <= current_time)
@@ -145,18 +145,18 @@
 }
 
 void SimulatedTimeControllerImpl::AdvanceTime(Timestamp target_time) {
-  rtc::CritScope time_lock(&time_lock_);
+  MutexLock time_lock(&time_lock_);
   RTC_DCHECK_GE(target_time, current_time_);
   current_time_ = target_time;
 }
 
 void SimulatedTimeControllerImpl::Register(SimulatedSequenceRunner* runner) {
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   runners_.push_back(runner);
 }
 
 void SimulatedTimeControllerImpl::Unregister(SimulatedSequenceRunner* runner) {
-  rtc::CritScope lock(&lock_);
+  MutexLock lock(&lock_);
   bool removed = RemoveByValue(&runners_, runner);
   RTC_CHECK(removed);
   RemoveByValue(&ready_runners_, runner);
diff --git a/test/time_controller/simulated_time_controller.h b/test/time_controller/simulated_time_controller.h
index 48112b3..6c6dbfa 100644
--- a/test/time_controller/simulated_time_controller.h
+++ b/test/time_controller/simulated_time_controller.h
@@ -21,9 +21,9 @@
 #include "api/units/timestamp.h"
 #include "modules/include/module.h"
 #include "modules/utility/include/process_thread.h"
-#include "rtc_base/critical_section.h"
 #include "rtc_base/fake_clock.h"
 #include "rtc_base/platform_thread_types.h"
+#include "rtc_base/synchronization/mutex.h"
 #include "rtc_base/synchronization/yield_policy.h"
 #include "rtc_base/thread_checker.h"
 
@@ -89,9 +89,9 @@
  private:
   const rtc::PlatformThreadId thread_id_;
   const std::unique_ptr<rtc::Thread> dummy_thread_ = rtc::Thread::Create();
-  rtc::CriticalSection time_lock_;
+  mutable Mutex time_lock_;
   Timestamp current_time_ RTC_GUARDED_BY(time_lock_);
-  rtc::CriticalSection lock_;
+  mutable Mutex lock_;
   std::vector<SimulatedSequenceRunner*> runners_ RTC_GUARDED_BY(lock_);
   // Used in RunReadyRunners() to keep track of ready runners that are to be
   // processed in a round robin fashion. the reason it's a member is so that