diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_thread_registry.h b/compiler-rt/lib/sanitizer_common/sanitizer_thread_registry.h
--- a/compiler-rt/lib/sanitizer_common/sanitizer_thread_registry.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_thread_registry.h
@@ -29,9 +29,10 @@
 };
 
 enum class ThreadType {
-  Regular, // Normal thread
-  Worker,  // macOS Grand Central Dispatch (GCD) worker thread
-  Fiber,   // Fiber
+  Regular,    // Normal thread
+  GcdWorker,  // Grand Central Dispatch (GCD) worker thread (Darwin)
+  Mach,       // Mach thread (Darwin)
+  Fiber,      // Fiber
 };
 
 // Generic thread context. Specific sanitizer tools may inherit from it.
diff --git a/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp b/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp
--- a/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp
+++ b/compiler-rt/lib/tsan/rtl/tsan_platform_mac.cpp
@@ -190,6 +190,17 @@
 #if !SANITIZER_GO
 void InitializeShadowMemoryPlatform() { }
 
+static void InitializeSpecialThread(pthread_t thread, ThreadType type) {
+  ThreadState *thr = cur_thread();
+  Processor *proc = ProcCreate();
+  ProcWire(proc, thr);
+  ThreadState *parent_thread_state = nullptr;  // No parent.
+  int tid = ThreadCreate(parent_thread_state, /*pc=*/0x0, (uptr)thread,
+                         /*detached=*/true);
+  CHECK_NE(tid, 0);
+  ThreadStart(thr, tid, GetTid(), type);
+}
+
 // On OS X, GCD worker threads are created without a call to pthread_create. We
 // need to properly register these threads with ThreadCreate and ThreadStart.
 // These threads don't have a parent thread, as they are created "spuriously".
@@ -200,31 +211,42 @@
 typedef void (*pthread_introspection_hook_t)(unsigned int event,
                                              pthread_t thread, void *addr,
                                              size_t size);
+enum {
+  PTHREAD_INTROSPECTION_THREAD_CREATE = 1,
+  PTHREAD_INTROSPECTION_THREAD_START,
+  PTHREAD_INTROSPECTION_THREAD_TERMINATE,
+  PTHREAD_INTROSPECTION_THREAD_DESTROY,
+};
 extern "C" pthread_introspection_hook_t pthread_introspection_hook_install(
     pthread_introspection_hook_t hook);
-static const uptr PTHREAD_INTROSPECTION_THREAD_CREATE = 1;
-static const uptr PTHREAD_INTROSPECTION_THREAD_TERMINATE = 3;
+
 static pthread_introspection_hook_t prev_pthread_introspection_hook;
 static void my_pthread_introspection_hook(unsigned int event, pthread_t thread,
                                           void *addr, size_t size) {
-  if (event == PTHREAD_INTROSPECTION_THREAD_CREATE) {
-    if (thread == pthread_self()) {
-      // The current thread is a newly created GCD worker thread.
-      ThreadState *thr = cur_thread();
-      Processor *proc = ProcCreate();
-      ProcWire(proc, thr);
-      ThreadState *parent_thread_state = nullptr;  // No parent.
-      int tid = ThreadCreate(parent_thread_state, 0, (uptr)thread, true);
-      CHECK_NE(tid, 0);
-      ThreadStart(thr, tid, GetTid(), ThreadType::Worker);
+  switch (event) {
+    case PTHREAD_INTROSPECTION_THREAD_CREATE: {
+      bool gcd_worker = (thread == pthread_self());
+      if (gcd_worker)
+        InitializeSpecialThread(thread, ThreadType::GcdWorker);
+      break;
     }
-  } else if (event == PTHREAD_INTROSPECTION_THREAD_TERMINATE) {
-    if (thread == pthread_self()) {
-      ThreadState *thr = cur_thread();
-      if (thr->tctx) {
-        DestroyThreadState();
-      }
+    case PTHREAD_INTROSPECTION_THREAD_START: {
+      CHECK(thread == pthread_self());
+      u32 tid = ThreadTid(cur_thread(), /*pc=*/0x0, (uptr)thread);
+      bool mach_thread = (tid == ThreadRegistry::kUnknownTid);
+      if (mach_thread)
+        InitializeSpecialThread(thread, ThreadType::Mach);
+      break;
     }
+    case PTHREAD_INTROSPECTION_THREAD_TERMINATE:
+      CHECK(thread == pthread_self());
+      // TODO(yln): when would the thread not have a context?
+      // TODO(yln): also: maybe this is a better check than the one above
+      if (cur_thread()->tctx)
+        DestroyThreadState();
+      break;
+    case PTHREAD_INTROSPECTION_THREAD_DESTROY:
+      break;
   }
 
   if (prev_pthread_introspection_hook != nullptr)
diff --git a/compiler-rt/lib/tsan/rtl/tsan_report.cpp b/compiler-rt/lib/tsan/rtl/tsan_report.cpp
--- a/compiler-rt/lib/tsan/rtl/tsan_report.cpp
+++ b/compiler-rt/lib/tsan/rtl/tsan_report.cpp
@@ -257,8 +257,11 @@
     Printf(" '%s'", rt->name);
   char thrbuf[kThreadBufSize];
   const char *thread_status = rt->running ? "running" : "finished";
-  if (rt->thread_type == ThreadType::Worker) {
-    Printf(" (tid=%zu, %s) is a GCD worker thread\n", rt->os_id, thread_status);
+  ThreadType type = rt->thread_type;
+  if (type == ThreadType::GcdWorker || type == ThreadType::Mach) {
+    auto *type_str = (type == ThreadType::GcdWorker) ? "GCD worker" : "Mach";
+    Printf(" (tid=%zu, %s) is a %s thread\n", rt->os_id, thread_status,
+           type_str);
     Printf("\n");
     Printf("%s", d.Default());
     return;