Index: lib/asan/asan_interceptors.cc
===================================================================
--- lib/asan/asan_interceptors.cc
+++ lib/asan/asan_interceptors.cc
@@ -138,6 +138,7 @@
 
 INTERCEPTOR(int, pthread_create, void *thread,
     void *attr, void *(*start_routine)(void*), void *arg) {
+  EnsureMainThreadIsCorrect();
   // Strict init-order checking in thread-hostile.
   if (flags()->strict_init_order)
     StopInitOrderChecking();
Index: lib/asan/asan_thread.h
===================================================================
--- lib/asan/asan_thread.h
+++ lib/asan/asan_thread.h
@@ -124,6 +124,8 @@
 u32 GetCurrentTidOrInvalid();
 AsanThread *FindThreadByStackAddress(uptr addr);
 
+// Used to handle fork().
+void EnsureMainThreadIsCorrect();
 }  // namespace __asan
 
 #endif  // ASAN_THREAD_H
Index: lib/asan/asan_thread.cc
===================================================================
--- lib/asan/asan_thread.cc
+++ lib/asan/asan_thread.cc
@@ -254,6 +254,12 @@
                                                    (void *)addr));
   return tctx ? tctx->thread : 0;
 }
+
+void EnsureMainThreadIsCorrect() {
+  AsanThreadContext *context = (AsanThreadContext*)AsanTSDGet();
+  if (context && (context->tid == 0))
+    context->os_id = GetTid();
+}
 }  // namespace __asan
 
 // --- Implementation of LSan-specific functions --- {{{1
@@ -283,4 +289,8 @@
 void UnlockThreadRegistry() {
   __asan::asanThreadRegistry().Unlock();
 }
+
+void EnsureMainThreadIsCorrect() {
+  __asan::EnsureMainThreadIsCorrect();
+}
 }  // namespace __lsan
Index: lib/lsan/lit_tests/TestCases/fork.cc
===================================================================
--- /dev/null
+++ lib/lsan/lit_tests/TestCases/fork.cc
@@ -0,0 +1,24 @@
+// Test that thread local data is handled correctly after forking without exec().
+// RUN: %clangxx_lsan %s -o %t
+// RUN: %t 2>&1
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+__thread void *thread_local_var;
+
+int main() {
+  int status = 0;
+  thread_local_var = malloc(1337);
+  pid_t pid = fork();
+  assert(pid >= 0);
+  if (pid > 0) {
+    waitpid(pid, &status, 0);
+    assert(WIFEXITED(status));
+    return WEXITSTATUS(status);
+  }
+  return 0;
+}
Index: lib/lsan/lit_tests/TestCases/fork_threaded.cc
===================================================================
--- /dev/null
+++ lib/lsan/lit_tests/TestCases/fork_threaded.cc
@@ -0,0 +1,44 @@
+// Test that thread local data is handled correctly after forking without
+// exec(). In this test leak checking is initiated from a non-main thread.
+// RUN: %clangxx_lsan %s -o %t
+// RUN: %t 2>&1
+
+#include <assert.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+__thread void *thread_local_var;
+
+void *exit_thread_func(void *arg) {
+  exit(0);
+}
+
+void ExitFromThread() {
+  pthread_t tid;
+  int res;
+  res = pthread_create(&tid, 0, exit_thread_func, 0);
+  assert(res == 0);
+  res = pthread_join(tid, 0);
+  assert(res == 0);
+}
+
+int main() {
+  int status = 0;
+  thread_local_var = malloc(1337);
+  pid_t pid = fork();
+  assert(pid >= 0);
+  if (pid > 0) {
+    waitpid(pid, &status, 0);
+    assert(WIFEXITED(status));
+    return WEXITSTATUS(status);
+  } else {
+    // Spawn a thread and call exit() from there, to check that we track main
+    // thread's pid correctly even if leak checking is initiated from another
+    // thread.
+    ExitFromThread();
+  }
+  return 0;
+}
Index: lib/lsan/lsan_common.h
===================================================================
--- lib/lsan/lsan_common.h
+++ lib/lsan/lsan_common.h
@@ -135,6 +135,8 @@
 bool GetThreadRangesLocked(uptr os_id, uptr *stack_begin, uptr *stack_end,
                            uptr *tls_begin, uptr *tls_end,
                            uptr *cache_begin, uptr *cache_end);
+// Needed to handle forked processed.
+void EnsureMainThreadIsCorrect();
 // If p points into a chunk that has been allocated to the user, returns its
 // user-visible address. Otherwise, returns 0.
 uptr PointsIntoChunk(void *p);
Index: lib/lsan/lsan_common.cc
===================================================================
--- lib/lsan/lsan_common.cc
+++ lib/lsan/lsan_common.cc
@@ -350,6 +350,7 @@
 }
 
 void DoLeakCheck() {
+  EnsureMainThreadIsCorrect();
   BlockingMutexLock l(&global_mutex);
   static bool already_done;
   CHECK(!already_done);
Index: lib/lsan/lsan_interceptors.cc
===================================================================
--- lib/lsan/lsan_interceptors.cc
+++ lib/lsan/lsan_interceptors.cc
@@ -218,6 +218,7 @@
 INTERCEPTOR(int, pthread_create, void *th, void *attr,
             void *(*callback)(void *), void *param) {
   Init();
+  EnsureMainThreadIsCorrect();
   __sanitizer_pthread_attr_t myattr;
   if (attr == 0) {
     pthread_attr_init(&myattr);
Index: lib/lsan/lsan_thread.h
===================================================================
--- lib/lsan/lsan_thread.h
+++ lib/lsan/lsan_thread.h
@@ -47,7 +47,7 @@
 u32 GetCurrentThread();
 void SetCurrentThread(u32 tid);
 ThreadContext *CurrentThreadContext();
-
+void EnsureMainThreadIsCorrect();
 }  // namespace __lsan
 
 #endif  // LSAN_THREAD_H
Index: lib/lsan/lsan_thread.cc
===================================================================
--- lib/lsan/lsan_thread.cc
+++ lib/lsan/lsan_thread.cc
@@ -123,6 +123,11 @@
   thread_registry->JoinThread(tid, /* arg */0);
 }
 
+void EnsureMainThreadIsCorrect() {
+  if (GetCurrentThread() == 0)
+    CurrentThreadContext()->os_id = GetTid();
+}
+
 ///// Interface to the common LSan module. /////
 
 bool GetThreadRangesLocked(uptr os_id, uptr *stack_begin, uptr *stack_end,