Index: lib/sanitizer_common/sanitizer_stoptheworld_mac.cc
===================================================================
--- lib/sanitizer_common/sanitizer_stoptheworld_mac.cc
+++ lib/sanitizer_common/sanitizer_stoptheworld_mac.cc
@@ -48,6 +48,16 @@
   CHECK(0 && "unimplemented");
 }
 
+#if defined(__x86_64__)
+#define THREAD_STATE_COUNT x86_THREAD_STATE64_COUNT
+#elif defined(__aarch64__)
+#define THREAD_STATE_COUNT ARM_THREAD_STATE64_COUNT
+#elif defined(__i386)
+#define THREAD_STATE_COUNT x86_THREAD_STATE32_COUNT
+#else
+#error "Unsupported architecture"
+#endif
+
 tid_t SuspendedThreadsListMac::GetThreadID(uptr index) const {
   CHECK_LT(index, threads_.size());
   return threads_[index].tid;
@@ -88,8 +98,7 @@
 }
 
 uptr SuspendedThreadsListMac::RegisterCount() const {
-  CHECK(0 && "unimplemented");
-  return 0;
+  return THREAD_STATE_COUNT;
 }
 } // namespace __sanitizer