Index: lib/tsan/rtl/tsan_interceptors_mac.cc
===================================================================
--- lib/tsan/rtl/tsan_interceptors_mac.cc
+++ lib/tsan/rtl/tsan_interceptors_mac.cc
@@ -21,6 +21,7 @@
 #include "tsan_interface_ann.h"
 
 #include <libkern/OSAtomic.h>
+#include <objc/objc-sync.h>
 
 #if defined(__has_include) && __has_include(<xpc/xpc.h>)
 #include <xpc/xpc.h>
@@ -318,17 +319,25 @@
   return (uptr)obj;
 }
 
-TSAN_INTERCEPTOR(int, objc_sync_enter, void *obj) {
+TSAN_INTERCEPTOR(int, objc_sync_enter, id obj) {
   SCOPED_TSAN_INTERCEPTOR(objc_sync_enter, obj);
+  if (!obj) return REAL(objc_sync_enter)(obj);
+  uptr addr = SyncAddressForObjCObject(obj);
+  MutexPreLock(thr, pc, addr, MutexFlagWriteReentrant);
   int result = REAL(objc_sync_enter)(obj);
-  if (obj) Acquire(thr, pc, SyncAddressForObjCObject(obj));
+  CHECK_EQ(result, OBJC_SYNC_SUCCESS);
+  MutexPostLock(thr, pc, addr, MutexFlagWriteReentrant);
   return result;
 }
 
-TSAN_INTERCEPTOR(int, objc_sync_exit, void *obj) {
+TSAN_INTERCEPTOR(int, objc_sync_exit, id obj) {
   SCOPED_TSAN_INTERCEPTOR(objc_sync_exit, obj);
-  if (obj) Release(thr, pc, SyncAddressForObjCObject(obj));
-  return REAL(objc_sync_exit)(obj);
+  if (!obj) return REAL(objc_sync_exit)(obj);
+  uptr addr = SyncAddressForObjCObject(obj);
+  MutexUnlock(thr, pc, addr);
+  int result = REAL(objc_sync_exit)(obj);
+  if (result != OBJC_SYNC_SUCCESS) MutexInvalidAccess(thr, pc, addr);
+  return result;
 }
 
 // On macOS, libc++ is always linked dynamically, so intercepting works the
Index: test/tsan/Darwin/objc-synchronize-cycle-tagged.mm
===================================================================
--- /dev/null
+++ test/tsan/Darwin/objc-synchronize-cycle-tagged.mm
@@ -0,0 +1,43 @@
+// RUN: %clangxx_tsan %s -o %t -framework Foundation -fobjc-arc %darwin_min_target_with_full_runtime_arc_support
+// RUN:     %run %t 6 2>&1 | FileCheck %s --check-prefix=SIX
+// RUN: not %run %t 7 2>&1 | FileCheck %s --check-prefix=SEVEN
+// XFAIL: *
+
+#import <Foundation/Foundation.h>
+
+static bool isTaggedPtr(id obj) {
+  uintptr_t ptr = (uintptr_t) obj;
+  return (ptr & 0x8000000000000001ull) != 0;
+}
+
+int main(int argc, char* argv[]) {
+  assert(argc == 2);
+  int arg = atoi(argv[0]);
+
+  @autoreleasepool {
+    NSObject* obj = [NSObject new];
+    NSObject* num1 = @7;
+    NSObject* num2 = [NSNumber numberWithInt:arg];
+
+    assert(!isTaggedPtr(obj));
+    assert(isTaggedPtr(num1) && isTaggedPtr(num2));
+
+    // obj -> num1 (includes num2)
+    @synchronized(obj) {
+      @synchronized(num1) {
+      }
+    }
+
+    // num2 -> obj1
+    @synchronized(num2) {
+      @synchronized(obj) {
+// SEVEN: ThreadSanitizer: lock-order-inversion (potential deadlock)
+      }
+    }
+  }
+
+  NSLog(@"PASS");
+// SIX-NOT: ThreadSanitizer
+// SIX: PASS
+  return 0;
+}
Index: test/tsan/Darwin/objc-synchronize-cycle.mm
===================================================================
--- /dev/null
+++ test/tsan/Darwin/objc-synchronize-cycle.mm
@@ -0,0 +1,31 @@
+// RUN: %clangxx_tsan %s -o %t -framework Foundation -fobjc-arc %darwin_min_target_with_full_runtime_arc_support
+// RUN:                                   not %run %t 2>&1 | FileCheck %s
+// RUN: %env_tsan_opts=detect_deadlocks=1 not %run %t 2>&1 | FileCheck %s
+// RUN: %env_tsan_opts=detect_deadlocks=0     %run %t 2>&1 | FileCheck %s --check-prefix=DISABLED
+
+#import <Foundation/Foundation.h>
+
+int main() {
+  @autoreleasepool {
+    NSObject* obj1 = [NSObject new];
+    NSObject* obj2 = [NSObject new];
+
+    // obj1 -> obj2
+    @synchronized(obj1) {
+      @synchronized(obj2) {
+      }
+    }
+
+    // obj1 -> obj1
+    @synchronized(obj2) {
+      @synchronized(obj1) {
+// CHECK: ThreadSanitizer: lock-order-inversion (potential deadlock)
+      }
+    }
+  }
+
+  NSLog(@"PASS");
+// DISABLED-NOT: ThreadSanitizer
+// DISABLED: PASS
+  return 0;
+}
Index: test/tsan/Darwin/objc-synchronize-nested-recursive.mm
===================================================================
--- /dev/null
+++ test/tsan/Darwin/objc-synchronize-nested-recursive.mm
@@ -0,0 +1,35 @@
+// RUN: %clangxx_tsan %s -o %t -framework Foundation -fobjc-arc %darwin_min_target_with_full_runtime_arc_support
+// RUN: %run %t 2>&1 | FileCheck %s
+
+#import <Foundation/Foundation.h>
+
+int main() {
+  @autoreleasepool {
+    NSObject* obj1 = [NSObject new];
+    NSObject* obj2 = [NSObject new];
+
+    @synchronized(obj1) {
+      @synchronized(obj1) {
+        NSLog(@"nested 1-1");
+// CHECK: nested 1-1
+      }
+    }
+
+    @synchronized(obj1) {
+      @synchronized(obj2) {
+        @synchronized(obj1) {
+          @synchronized(obj2) {
+            NSLog(@"nested 1-2-1-2");
+// CHECK: nested 1-2-1-2
+          }
+        }
+      }
+    }
+
+  }
+
+  NSLog(@"PASS");
+// CHECK-NOT: ThreadSanitizer
+// CHECK: PASS
+  return 0;
+}