Index: compiler-rt/trunk/lib/lsan/lsan_common.h
===================================================================
--- compiler-rt/trunk/lib/lsan/lsan_common.h
+++ compiler-rt/trunk/lib/lsan/lsan_common.h
@@ -127,6 +127,7 @@
 // Functions called from the parent tool.
 void InitCommonLsan();
 void DoLeakCheck();
+void DisableCounterUnderflow();
 bool DisabledInThisThread();
 
 // Used to implement __lsan::ScopedDisabler.
Index: compiler-rt/trunk/lib/lsan/lsan_common.cc
===================================================================
--- compiler-rt/trunk/lib/lsan/lsan_common.cc
+++ compiler-rt/trunk/lib/lsan/lsan_common.cc
@@ -32,20 +32,15 @@
 // also to protect the global list of root regions.
 BlockingMutex global_mutex(LINKER_INITIALIZED);
 
-__attribute__((tls_model("initial-exec")))
-THREADLOCAL int disable_counter;
-bool DisabledInThisThread() { return disable_counter > 0; }
-void DisableInThisThread() { disable_counter++; }
-void EnableInThisThread() {
-  if (!disable_counter && common_flags()->detect_leaks) {
+Flags lsan_flags;
+
+void DisableCounterUnderflow() {
+  if (common_flags()->detect_leaks) {
     Report("Unmatched call to __lsan_enable().\n");
     Die();
   }
-  disable_counter--;
 }
 
-Flags lsan_flags;
-
 void Flags::SetDefaults() {
 #define LSAN_FLAG(Type, Name, DefaultValue, Description) Name = DefaultValue;
 #include "lsan_flags.inc"
Index: compiler-rt/trunk/lib/lsan/lsan_common_linux.cc
===================================================================
--- compiler-rt/trunk/lib/lsan/lsan_common_linux.cc
+++ compiler-rt/trunk/lib/lsan/lsan_common_linux.cc
@@ -34,6 +34,17 @@
   return LibraryNameIs(full_name, kLinkerName);
 }
 
+__attribute__((tls_model("initial-exec")))
+THREADLOCAL int disable_counter;
+bool DisabledInThisThread() { return disable_counter > 0; }
+void DisableInThisThread() { disable_counter++; }
+void EnableInThisThread() {
+  if (disable_counter == 0) {
+    DisableCounterUnderflow();
+  }
+  disable_counter--;
+}
+
 void InitializePlatformSpecificModules() {
   ListOfModules modules;
   modules.init();
Index: compiler-rt/trunk/lib/lsan/lsan_common_mac.cc
===================================================================
--- compiler-rt/trunk/lib/lsan/lsan_common_mac.cc
+++ compiler-rt/trunk/lib/lsan/lsan_common_mac.cc
@@ -12,12 +12,53 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "sanitizer_common/sanitizer_allocator_internal.h"
 #include "sanitizer_common/sanitizer_platform.h"
 #include "lsan_common.h"
 
 #if CAN_SANITIZE_LEAKS && SANITIZER_MAC
+
+#include <pthread.h>
+
 namespace __lsan {
 
+static pthread_key_t key;
+static pthread_once_t key_once = PTHREAD_ONCE_INIT;
+
+static void make_tls_key() { CHECK_EQ(pthread_key_create(&key, NULL), 0); }
+
+static int *get_tls_val(bool allocate) {
+  pthread_once(&key_once, make_tls_key);
+
+  int *ptr = (int *)pthread_getspecific(key);
+  if (ptr == NULL && allocate) {
+    ptr = (int *)InternalAlloc(sizeof(*ptr));
+    *ptr = 0;
+    pthread_setspecific(key, ptr);
+  }
+
+  return ptr;
+}
+
+bool DisabledInThisThread() {
+  int *disable_counter = get_tls_val(false);
+  return disable_counter ? *disable_counter > 0 : false;
+}
+
+void DisableInThisThread() {
+  int *disable_counter = get_tls_val(true);
+
+  ++*disable_counter;
+}
+
+void EnableInThisThread() {
+  int *disable_counter = get_tls_val(true);
+  if (*disable_counter == 0) {
+    DisableCounterUnderflow();
+  }
+  --*disable_counter;
+}
+
 void InitializePlatformSpecificModules() {
   CHECK(0 && "unimplemented");
 }