diff --git a/internal/platform/implementation/apple/BUILD b/internal/platform/implementation/apple/BUILD
index 182787fe..50b68b35 100644
--- a/internal/platform/implementation/apple/BUILD
+++ b/internal/platform/implementation/apple/BUILD
@@ -347,6 +347,7 @@ cc_test(
         ":Platform_cc",
         "//internal/platform/implementation/g3:crypto",
         "@com_github_protobuf_matchers//protobuf-matchers",
+        "@com_google_absl//absl/base:core_headers",
         "@com_google_absl//absl/synchronization",
         "@com_google_absl//absl/time",
         "@com_google_googletest//:gtest_main",
diff --git a/internal/platform/implementation/apple/mutex.h b/internal/platform/implementation/apple/mutex.h
index 3a7890b2..210aa883 100644
--- a/internal/platform/implementation/apple/mutex.h
+++ b/internal/platform/implementation/apple/mutex.h
@@ -15,6 +15,7 @@
 #ifndef PLATFORM_IMPL_APPLE_MUTEX_H_
 #define PLATFORM_IMPL_APPLE_MUTEX_H_
 
+#include "absl/base/thread_annotations.h"
 #include "absl/synchronization/mutex.h"
 #include "internal/platform/implementation/mutex.h"
 
@@ -36,6 +37,10 @@ class ABSL_LOCKABLE Mutex : public api::Mutex {
   }
   void Unlock() ABSL_UNLOCK_FUNCTION() override { mutex_.Unlock(); }
 
+  void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() override {
+    mutex_.AssertHeld();
+  }
+
  private:
   friend class ConditionVariable;
   absl::Mutex mutex_;
@@ -65,6 +70,12 @@ class ABSL_LOCKABLE RecursiveMutex : public api::Mutex {
     }
   }
 
+  void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() override {
+#ifndef NDEBUG
+    assert(thread_id_.load(std::memory_order_acquire) == ThreadId());
+#endif
+  }
+
  private:
   static inline intptr_t ThreadId() {
     ABSL_CONST_INIT thread_local int per_thread = 0;
diff --git a/internal/platform/implementation/apple/mutex_test.cc b/internal/platform/implementation/apple/mutex_test.cc
index 4a9bded4..4ebadce0 100644
--- a/internal/platform/implementation/apple/mutex_test.cc
+++ b/internal/platform/implementation/apple/mutex_test.cc
@@ -15,9 +15,8 @@
 #include "internal/platform/implementation/apple/mutex.h"
 
 #include "gtest/gtest.h"
-#include "absl/synchronization/mutex.h"
+#include "absl/base/thread_annotations.h"
 #include "absl/synchronization/notification.h"
-#include "absl/time/clock.h"
 #include "absl/time/time.h"
 #include "thread/fiber/fiber.h"
 
@@ -85,6 +84,36 @@ TEST(MutexTest, RecursiveLockingForNestedWorks) {
   f.Join();
 }
 
+TEST(MutexTest, AssertHeld) {
+  Mutex mutex;
+  mutex.Lock();
+  mutex.AssertHeld();
+  mutex.Unlock();
+}
+
+TEST(MutexTest, RecursiveAssertHeld) ABSL_NO_THREAD_SAFETY_ANALYSIS {
+  RecursiveMutex mutex;
+  mutex.Lock();
+  mutex.AssertHeld();
+  mutex.Lock();
+  mutex.AssertHeld();
+  mutex.Unlock();
+  mutex.AssertHeld();
+  mutex.Unlock();
+}
+
+#if !defined(NDEBUG) && defined(GTEST_HAS_DEATH_TEST)
+TEST(MutexDeathTest, MutexAssertHeldWithoutLock) {
+  Mutex mutex;
+  EXPECT_DEATH(mutex.AssertHeld(), "");
+}
+
+TEST(MutexDeathTest, RecursiveMutexAssertHeldWithoutLock) {
+  RecursiveMutex mutex;
+  EXPECT_DEATH(mutex.AssertHeld(), "");
+}
+#endif  // !defined(NDEBUG) && defined(GTEST_HAS_DEATH_TEST)
+
 }  // namespace
 }  // namespace apple
 }  // namespace nearby
diff --git a/internal/platform/implementation/g3/mutex.h b/internal/platform/implementation/g3/mutex.h
index c808731f..0b9e9b2f 100644
--- a/internal/platform/implementation/g3/mutex.h
+++ b/internal/platform/implementation/g3/mutex.h
@@ -15,6 +15,7 @@
 #ifndef PLATFORM_IMPL_G3_MUTEX_H_
 #define PLATFORM_IMPL_G3_MUTEX_H_
 
+#include "absl/base/thread_annotations.h"
 #include "absl/synchronization/mutex.h"
 #include "internal/platform/implementation/mutex.h"
 #include "internal/platform/implementation/shared/posix_mutex.h"
@@ -35,8 +36,13 @@ class ABSL_LOCKABLE Mutex : public api::Mutex {
     mutex_.Lock();
     if (!check_) mutex_.ForgetDeadlockInfo();
   }
+
   void Unlock() ABSL_UNLOCK_FUNCTION() override { mutex_.Unlock(); }
 
+  void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() override {
+    mutex_.AssertHeld();
+  }
+
  private:
   friend class ConditionVariable;
   absl::Mutex mutex_;
diff --git a/internal/platform/implementation/mutex.h b/internal/platform/implementation/mutex.h
index 622f1056..d226cc64 100644
--- a/internal/platform/implementation/mutex.h
+++ b/internal/platform/implementation/mutex.h
@@ -45,6 +45,8 @@ class ABSL_LOCKABLE Mutex {
 
   virtual void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION() = 0;
   virtual void Unlock() ABSL_UNLOCK_FUNCTION() = 0;
+  // Assert that this mutex is held by the calling thread.
+  virtual void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() {}
 };
 
 }  // namespace api
diff --git a/internal/platform/implementation/shared/posix_mutex.h b/internal/platform/implementation/shared/posix_mutex.h
index b1d15d0a..183a14d8 100644
--- a/internal/platform/implementation/shared/posix_mutex.h
+++ b/internal/platform/implementation/shared/posix_mutex.h
@@ -29,6 +29,7 @@ class ABSL_LOCKABLE Mutex : public api::Mutex {
 
   void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION() override;
   void Unlock() ABSL_UNLOCK_FUNCTION() override;
+  void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() override {}
 
  private:
   friend class ConditionVariable;
diff --git a/internal/platform/implementation/windows/mutex.h b/internal/platform/implementation/windows/mutex.h
index 006293e9..44488a23 100644
--- a/internal/platform/implementation/windows/mutex.h
+++ b/internal/platform/implementation/windows/mutex.h
@@ -52,6 +52,12 @@ class ABSL_LOCKABLE Mutex : public api::Mutex {
     }
   }
 
+  void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() override {
+    if (mode_ == Mode::kRegular || mode_ == Mode::kRegularNoCheck) {
+      mutex_.AssertHeld();
+    }
+  }
+
   absl::Mutex& GetMutex() { return mutex_; }
   std::recursive_mutex& GetRecursiveMutex() { return recursive_mutex_; }
 
diff --git a/internal/platform/mutex.h b/internal/platform/mutex.h
index 6ce81a69..f1c5808f 100644
--- a/internal/platform/mutex.h
+++ b/internal/platform/mutex.h
@@ -41,6 +41,7 @@ class ABSL_LOCKABLE Mutex final {
 
   void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION() { impl_->Lock(); }
   void Unlock() ABSL_UNLOCK_FUNCTION() { impl_->Unlock(); }
+  void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() { impl_->AssertHeld(); }
 
  private:
   friend class ConditionVariable;
@@ -65,6 +66,7 @@ class ABSL_LOCKABLE RecursiveMutex final {
 
   void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION() { impl_->Lock(); }
   void Unlock() ABSL_UNLOCK_FUNCTION() { impl_->Unlock(); }
+  void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() { impl_->AssertHeld(); }
 
  private:
   friend class MutexLock;
diff --git a/internal/platform/mutex_test.cc b/internal/platform/mutex_test.cc
index 0e22212c..8e70e65d 100644
--- a/internal/platform/mutex_test.cc
+++ b/internal/platform/mutex_test.cc
@@ -14,11 +14,13 @@
 
 #include "internal/platform/mutex.h"
 
+#include <atomic>
+
 #include "gtest/gtest.h"
+#include "absl/base/thread_annotations.h"
 #include "absl/synchronization/mutex.h"
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
-#include "internal/platform/condition_variable.h"
 #include "internal/platform/single_thread_executor.h"
 
 namespace nearby {
@@ -111,5 +113,38 @@ TEST_F(MutexTest, DoubleLockIsNotDeadlock) {
   VerifyStepReached(2);
 }
 
+TEST_F(MutexTest, AssertHeld) {
+  Mutex mutex;
+  mutex.Lock();
+  mutex.AssertHeld();
+  mutex.Unlock();
+}
+
+TEST_F(MutexTest, RecursiveAssertHeld) ABSL_NO_THREAD_SAFETY_ANALYSIS {
+  RecursiveMutex mutex;
+  mutex.Lock();
+  mutex.AssertHeld();
+  mutex.Lock();
+  mutex.AssertHeld();
+  mutex.Unlock();
+  mutex.AssertHeld();
+  mutex.Unlock();
+}
+
+#ifndef NDEBUG
+using MutexDeathTest = MutexTest;
+// Mutex death test may fail on some platforms.
+TEST_F(MutexDeathTest, DISABLED_MutexAssertHeldWithoutLock) {
+  Mutex mutex;
+  EXPECT_DEATH(mutex.AssertHeld(), "");
+}
+
+// RecursiveMutex death test may fail on some platforms.
+TEST_F(MutexDeathTest, DISABLED_RecursiveMutexAssertHeldWithoutLock) {
+  RecursiveMutex mutex;
+  EXPECT_DEATH(mutex.AssertHeld(), "");
+}
+#endif
+
 }  // namespace
 }  // namespace nearby