Index: compiler-rt/trunk/lib/tsan/rtl/tsan_platform_mac.cc
===================================================================
--- compiler-rt/trunk/lib/tsan/rtl/tsan_platform_mac.cc
+++ compiler-rt/trunk/lib/tsan/rtl/tsan_platform_mac.cc
@@ -91,7 +91,11 @@
 // handler will try to access the unmapped ThreadState.
 void cur_thread_finalize() {
   uptr thread_identity = (uptr)pthread_self();
-  CHECK_NE(thread_identity, main_thread_identity);
+  if (thread_identity == main_thread_identity) {
+    // Calling dispatch_main() or xpc_main() actually invokes pthread_exit to
+    // exit the main thread. Let's keep the main thread's ThreadState.
+    return;
+  }
   ThreadState **fake_tls = (ThreadState **)MemToShadow(thread_identity);
   internal_munmap(*fake_tls, sizeof(ThreadState));
   *fake_tls = nullptr;
Index: compiler-rt/trunk/test/tsan/Darwin/dispatch_main.mm
===================================================================
--- compiler-rt/trunk/test/tsan/Darwin/dispatch_main.mm
+++ compiler-rt/trunk/test/tsan/Darwin/dispatch_main.mm
@@ -0,0 +1,38 @@
+// Check that we don't crash when dispatch_main calls pthread_exit which
+// quits the main thread.
+
+// RUN: %clang_tsan %s -o %t -framework Foundation
+// RUN: %env_tsan_opts=ignore_interceptors_accesses=1 %run %t 2>&1 | FileCheck %s
+
+#import <Foundation/Foundation.h>
+
+int main() {
+  NSLog(@"Hello world");
+
+  dispatch_queue_t q = dispatch_queue_create("my.queue", DISPATCH_QUEUE_SERIAL);
+
+  dispatch_async(q, ^{
+    NSLog(@"1");
+  });
+
+  dispatch_async(q, ^{
+    NSLog(@"2");
+  });
+
+  dispatch_async(q, ^{
+    NSLog(@"3");
+
+    dispatch_async(dispatch_get_main_queue(), ^{
+      NSLog(@"Done.");
+      sleep(1);
+      exit(0);
+    });
+  });
+
+  dispatch_main();
+}
+
+// CHECK: Hello world
+// CHECK: Done.
+// CHECK-NOT: WARNING: ThreadSanitizer
+// CHECK-NOT: CHECK failed