Index: lib/tsan/rtl/tsan_report.h
===================================================================
--- lib/tsan/rtl/tsan_report.h
+++ lib/tsan/rtl/tsan_report.h
@@ -90,7 +90,7 @@
   uptr os_id;
   bool running;
   char *name;
-  int parent_tid;
+  u32 parent_tid;
   ReportStack *stack;
 };
 
Index: lib/tsan/rtl/tsan_report.cc
===================================================================
--- lib/tsan/rtl/tsan_report.cc
+++ lib/tsan/rtl/tsan_report.cc
@@ -235,9 +235,15 @@
   if (rt->name && rt->name[0] != '\0')
     Printf(" '%s'", rt->name);
   char thrbuf[kThreadBufSize];
-  Printf(" (tid=%zu, %s) created by %s",
-    rt->os_id, rt->running ? "running" : "finished",
-    thread_name(thrbuf, rt->parent_tid));
+  const char *thread_status = rt->running ? "running" : "finished";
+  if (rt->parent_tid == kInvalidTid) {
+    Printf(" (tid=%zu, %s) is a GCD worker thread\n", rt->os_id, thread_status);
+    Printf("\n");
+    Printf("%s", d.EndThreadDescription());
+    return;
+  }
+  Printf(" (tid=%zu, %s) created by %s", rt->os_id, thread_status,
+         thread_name(thrbuf, rt->parent_tid));
   if (rt->stack)
     Printf(" at:");
   Printf("\n");
Index: test/tsan/Darwin/workerthreads.mm
===================================================================
--- test/tsan/Darwin/workerthreads.mm
+++ test/tsan/Darwin/workerthreads.mm
@@ -0,0 +1,43 @@
+// RUN: %clang_tsan %s -o %t -framework Foundation
+// RUN: %deflake %run %t 2>&1 | FileCheck %s
+
+#import <Foundation/Foundation.h>
+
+#import "../test.h"
+
+long global;
+
+int main() {
+  fprintf(stderr, "Hello world.\n");
+  print_address("addr=", 1, &global);
+  barrier_init(&barrier, 2);
+
+  global = 42;
+  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+    global = 43;
+    barrier_wait(&barrier);
+  });
+
+  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+    barrier_wait(&barrier);
+    global = 44;
+
+    dispatch_sync(dispatch_get_main_queue(), ^{
+      CFRunLoopStop(CFRunLoopGetCurrent());
+    });
+  });
+
+  CFRunLoopRun();
+  fprintf(stderr, "Done.\n");
+}
+
+// CHECK: Hello world.
+// CHECK: WARNING: ThreadSanitizer: data race
+// CHECK: Write of size 8
+// CHECK: Previous write of size 8
+// CHECK: Location is global
+// CHECK: Thread {{.*}} is a GCD worker thread
+// CHECK-NOT: failed to restore the stack
+// CHECK: Thread {{.*}} is a GCD worker thread
+// CHECK-NOT: failed to restore the stack
+// CHECK: Done.