diff --git a/src/mzscheme/gc2/sighand.c b/src/mzscheme/gc2/sighand.c
index eea8aeef28..6512d3b61e 100644
--- a/src/mzscheme/gc2/sighand.c
+++ b/src/mzscheme/gc2/sighand.c
@@ -1,6 +1,6 @@
 /* 
    Provides:
-      initialize_signal_handler();
+      initialize_signal_handler(GCTYPE *gc)
       remove_signal_handler();
    Requires:
       generations_available - mutable int, Windows only
@@ -147,7 +147,11 @@ void fault_handler(int sn, siginfo_t *si, void *ctx)
 static void initialize_signal_handler(GCTYPE *gc)
 {
 # ifdef NEED_OSX_MACH_HANDLER
-  macosx_init_exception_handler();
+#  if defined(MZ_USE_PLACES) && defined(MZ_PRECISE_GC)
+  macosx_init_exception_handler(MASTERGC == 0);
+#  else
+  macosx_init_exception_handler(1);
+#  endif
 # endif
 # ifdef NEED_SIGACTION
   {
diff --git a/src/mzscheme/gc2/vm_osx.c b/src/mzscheme/gc2/vm_osx.c
index 6d01b12103..4cf8233177 100644
--- a/src/mzscheme/gc2/vm_osx.c
+++ b/src/mzscheme/gc2/vm_osx.c
@@ -35,6 +35,64 @@ static int designate_modified(void *p);
 int designate_modified(void *p);
 #endif
 
+#if defined(MZ_USE_PLACES) && defined (MZ_PRECISE_GC)
+typedef struct OSXThreadData {
+  struct OSXThreadData *next;
+  mach_port_t thread_port_id;
+  Thread_Local_Variables  *tlvs;
+} OSXThreadData; 
+
+/* static const int OSX_THREAD_TABLE_SIZE = 256; */
+#define OSX_THREAD_TABLE_SIZE 256
+static OSXThreadData *osxthreads[OSX_THREAD_TABLE_SIZE];
+static pthread_mutex_t osxthreadsmutex = PTHREAD_MUTEX_INITIALIZER;
+
+static Thread_Local_Variables *get_mach_thread_tlvs(mach_port_t threadid) {
+  int index = threadid % OSX_THREAD_TABLE_SIZE;
+  OSXThreadData *thread;
+  Thread_Local_Variables *tlvs = NULL;
+
+  pthread_mutex_lock(&osxthreadsmutex);
+  {
+    for (thread = osxthreads[index]; thread; thread = thread->next)
+    {
+      if (thread->thread_port_id == threadid) {
+        tlvs = thread->tlvs;
+        break;
+      }
+    }
+  }
+  pthread_mutex_unlock(&osxthreadsmutex);
+
+  return tlvs;
+}
+
+static void set_thread_locals_from_mach_thread_id(mach_port_t threadid) {
+  Thread_Local_Variables *tlvs = get_mach_thread_tlvs(threadid);
+#ifdef USE_THREAD_LOCAL
+  pthread_setspecific(scheme_thread_local_key, tlvs);
+#endif
+}
+
+static void register_mach_thread() {
+  mach_port_t thread_self = mach_thread_self();
+  int index = thread_self % OSX_THREAD_TABLE_SIZE;
+  OSXThreadData * thread = malloc(sizeof(OSXThreadData));
+
+  thread->thread_port_id = thread_self;
+  thread->tlvs = scheme_get_thread_local_variables();
+
+  /* PUSH thread record onto osxthreads datastructure */
+  pthread_mutex_lock(&osxthreadsmutex);
+  {
+    thread->next = osxthreads[index];
+    osxthreads[index] = thread;
+  }
+  pthread_mutex_unlock(&osxthreadsmutex);
+}
+
+#endif
+
 #if defined(__POWERPC__)
 # define ARCH_thread_state_t ppc_thread_state_t
 # define ARCH_THREAD_STATE PPC_THREAD_STATE
@@ -227,6 +285,11 @@ kern_return_t GC_catch_exception_raise(mach_port_t port,
                            &exc_state_count);
     p = (void *)exc_state.__faultvaddr;
 #endif
+
+#if defined(MZ_USE_PLACES) && defined (MZ_PRECISE_GC)
+  set_thread_locals_from_mach_thread_id(thread_port);
+#endif
+
     if (designate_modified(p))
       return KERN_SUCCESS;
     else
@@ -306,14 +369,22 @@ void GC_attach_current_thread_exceptions_to_handler()
     GCPRINT(GCOUTF, "Couldn't set exception ports: %s\n", mach_error_string(retval));
     abort();
   }
+#if defined(MZ_USE_PLACES) && defined (MZ_PRECISE_GC)
+  register_mach_thread();
+#endif
 }
 
 /* this initializes the subsystem (sets the exception port, starts the
    exception handling thread, etc) */
-static void macosx_init_exception_handler() 
+static void macosx_init_exception_handler(int isMASTERGC)
 {
   kern_return_t retval;
 
+  if (!isMASTERGC) {
+    GC_attach_current_thread_exceptions_to_handler();
+    return;
+  }
+
   if(!task_self) task_self = mach_task_self();
 
   /* allocate the port we're going to get exceptions on */
diff --git a/src/mzscheme/src/mzrt.c b/src/mzscheme/src/mzrt.c
index 4cdad99dc9..2cf35c6197 100644
--- a/src/mzscheme/src/mzrt.c
+++ b/src/mzscheme/src/mzrt.c
@@ -196,6 +196,17 @@ mz_proc_thread* mzrt_proc_first_thread_init() {
 
 mz_proc_thread* mz_proc_thread_create(mz_proc_thread_start start_proc, void* data) {
   mz_proc_thread *thread = (mz_proc_thread*)malloc(sizeof(mz_proc_thread));
+  pthread_attr_t *attr;
+
+#ifdef OS_X
+  pthread_attr_t attr_storage;
+  attr = &attr_storage;
+  pthread_attr_init(attr);
+  pthread_attr_setstacksize(attr, 8*1024*1024); /*8MB*/
+#else
+  attr = NULL;
+#endif
+
 #ifdef MZ_PRECISE_GC
   mzrt_thread_stub_data *stub_data = (mzrt_thread_stub_data*)malloc(sizeof(mzrt_thread_stub_data));
   thread->mbox = pt_mbox_create();
@@ -205,13 +216,13 @@ mz_proc_thread* mz_proc_thread_create(mz_proc_thread_start start_proc, void* dat
 #   ifdef WIN32
   thread->threadid = CreateThread(NULL, 0, start_proc, data, 0, NULL);
 #   else
-  pthread_create(&thread->threadid, NULL, mzrt_thread_stub, stub_data);
+  pthread_create(&thread->threadid, attr, mzrt_thread_stub, stub_data);
 #   endif
 #else
 #   ifdef WIN32
   thread->threadid = GC_CreateThread(NULL, 0, start_proc, data, 0, NULL);
 #   else
-  GC_pthread_create(&thread->threadid, NULL, start_proc, data);
+  GC_pthread_create(&thread->threadid, attr, start_proc, data);
 #   endif
 #endif
   return thread;