diff --git a/src/compiler/generic/objdef.lisp b/src/compiler/generic/objdef.lisp
index d768bca..dd45bea 100644
--- a/src/compiler/generic/objdef.lisp
+++ b/src/compiler/generic/objdef.lisp
@@ -356,7 +356,7 @@
   (real :c-type "double" :length #!-x86-64 2 #!+x86-64 1)
   (imag :c-type "double" :length #!-x86-64 2 #!+x86-64 1))
 
-#!+(and sb-lutex sb-thread)
+#!+(and sb-lutex sb-thread (not sb-mach-lutex))
 (define-primitive-object (lutex
                           :lowtag other-pointer-lowtag
                           :widetag lutex-widetag
@@ -372,6 +372,17 @@
   (condition-variable :c-type "pthread_cond_t *"
                       :length 1))
 
+#!+(and sb-lutex sb-thread sb-mach-lutex)
+(define-primitive-object (lutex
+                          :lowtag other-pointer-lowtag
+                          :widetag lutex-widetag
+                          :alloc-trans %make-lutex)
+  (gen :c-type "long" :length 1)
+  (live :c-type "long" :length 1)
+  (next :c-type "struct lutex *" :length 1)
+  (prev :c-type "struct lutex *" :length 1)
+  (semaphore :c-type "unsigned long" :length 1))
+
 ;;; this isn't actually a lisp object at all, it's a c structure that lives
 ;;; in c-land.  However, we need sight of so many parts of it from Lisp that
 ;;; it makes sense to define it here anyway, so that the GENESIS machinery
diff --git a/src/runtime/GNUmakefile b/src/runtime/GNUmakefile
index cfaac20..51e2688 100644
--- a/src/runtime/GNUmakefile
+++ b/src/runtime/GNUmakefile
@@ -41,7 +41,7 @@ include Config
 COMMON_SRC = alloc.c backtrace.c breakpoint.c coreparse.c \
 	dynbind.c funcall.c gc-common.c globals.c interr.c interrupt.c \
 	largefile.c monitor.c os-common.c parse.c print.c purify.c \
-	pthread-futex.c pthread-lutex.c \
+	pthread-futex.c pthread-lutex.c mach-lutex.c \
 	regnames.c run-program.c runtime.c save.c search.c \
 	thread.c time.c util.c validate.c vars.c wrap.c	
 
diff --git a/src/runtime/coreparse.c b/src/runtime/coreparse.c
index 1757444..e527bf1 100644
--- a/src/runtime/coreparse.c
+++ b/src/runtime/coreparse.c
@@ -38,7 +38,11 @@
 /* lutex stuff */
 #if defined(LISP_FEATURE_SB_THREAD) && defined(LISP_FEATURE_SB_LUTEX)
 #include "genesis/sap.h"
-#include "pthread-lutex.h"
+# ifdef LISP_FEATURE_SB_MACH_LUTEX
+#  include "mach-lutex.h"
+# else
+#  include "pthread-lutex.h"
+# endif
 #endif
 
 
diff --git a/src/runtime/gencgc.c b/src/runtime/gencgc.c
index 5bd67c8..6e006e5 100644
--- a/src/runtime/gencgc.c
+++ b/src/runtime/gencgc.c
@@ -53,7 +53,11 @@
 #include "genesis/layout.h"
 #include "gencgc.h"
 #if defined(LUTEX_WIDETAG)
-#include "pthread-lutex.h"
+# ifdef LISP_FEATURE_SB_MACH_LUTEX
+#  include "mach-lutex.h"
+# else
+#  include "pthread-lutex.h"
+# endif
 #endif
 
 /* forward declarations */
diff --git a/src/runtime/mach-lutex.c b/src/runtime/mach-lutex.c
new file mode 100644
index 0000000..7604eac
--- /dev/null
+++ b/src/runtime/mach-lutex.c
@@ -0,0 +1,174 @@
+#include "sbcl.h"
+
+#if defined(LISP_FEATURE_SB_THREAD) && defined(LISP_FEATURE_SB_MACH_LUTEX)  && defined(LISP_FEATURE_SB_MACH_LUTEX)
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include <mach/semaphore.h>
+#include <mach/task.h>
+
+#include "runtime.h"
+#include "arch.h"
+#include "target-arch-os.h"
+#include "os.h"
+#include "mach-lutex.h"
+#include "gencgc.h"
+
+#include "genesis/lutex.h"
+
+#if 1
+# define lutex_assert(ex)                                              \
+do {                                                                   \
+    if (!(ex)) lutex_abort();                                          \
+} while (0)
+# define lutex_assert_verbose(ex, fmt, ...)                            \
+do {                                                                   \
+    if (!(ex)) {                                                       \
+        fprintf(stderr, fmt, ## __VA_ARGS__);                          \
+        lutex_abort();                                                 \
+    }                                                                  \
+} while (0)
+#else
+# define lutex_assert(ex)
+# define lutex_assert_verbose(ex, fmt, ...)
+#endif
+
+#define lutex_abort()                                                  \
+  lose("Lutex assertion failure, file \"%s\", line %d\n", __FILE__, __LINE__)
+
+static semaphore_t lutex_register_semaphore = 0;
+
+int
+lutex_init (tagged_lutex_t tagged_lutex)
+{
+    int ret;
+    struct lutex *lutex = (struct lutex*) native_pointer(tagged_lutex);
+    task_t self = mach_task_self();
+    unsigned sem;
+    if (!lutex_register_semaphore) {
+        int ret = semaphore_create(self, &sem, SYNC_POLICY_FIFO, 1);
+        lutex_assert(!ret);
+
+        if (lutex_register_semaphore) // TODO: compare-and-swap
+            semaphore_destroy(self, sem);
+        else
+            lutex_register_semaphore = sem;
+    }
+
+    ret = semaphore_create(self, &sem, SYNC_POLICY_FIFO, 1);
+    lutex->semaphore = sem;
+    /* only binary semaphores for now; while this results in spurious wake-ups in condvars,
+     *  that's acceptable fpr condvars.
+     */
+    lutex_assert(!ret);
+
+    ret = semaphore_wait(lutex_register_semaphore);
+    lutex_assert(!ret);
+
+    gencgc_register_lutex(lutex);
+
+    ret = semaphore_signal(lutex_register_semaphore);
+    lutex_assert(!ret);
+
+    return ret;
+}
+
+int
+lutex_wait (tagged_lutex_t tagged_queue_lutex, tagged_lutex_t tagged_mutex_lutex)
+{
+    int ret;
+    struct lutex *queue_lutex = (struct lutex*) native_pointer(tagged_queue_lutex);
+    struct lutex *mutex_lutex = (struct lutex*) native_pointer(tagged_mutex_lutex);
+
+    ret = semaphore_wait_signal(queue_lutex->semaphore,
+                                mutex_lutex->semaphore);
+    if (KERN_ABORTED == ret) return ret;
+    lutex_assert_verbose(!ret, "ret: %d\n", ret);
+
+    semaphore_wait(mutex_lutex->semaphore);
+    lutex_assert(!ret);
+
+    return ret;
+}
+
+int
+lutex_wake (tagged_lutex_t tagged_lutex, int n)
+{
+    int ret = 0;
+    struct lutex *lutex = (struct lutex*) native_pointer(tagged_lutex);
+
+    if (n >= ((1 << 29) - 1)) {
+        ret = semaphore_signal_all(lutex->semaphore);
+        lutex_assert(!ret);
+    } else {
+        while (n--) {
+            ret = semaphore_signal_thread(lutex->semaphore, 0);
+            if (KERN_NOT_WAITING == ret) return 0;
+
+            lutex_assert(!ret);
+        }
+    }
+
+    return ret;
+}
+
+int
+lutex_lock (tagged_lutex_t tagged_lutex)
+{
+    int ret = 0;
+    struct lutex *lutex = (struct lutex*) native_pointer(tagged_lutex);
+
+    do
+        ret = semaphore_wait(lutex->semaphore);
+    while (ret == KERN_ABORTED);
+
+    lutex_assert_verbose(!ret, "ret: %d\n", ret);
+
+    return ret;
+}
+
+int
+lutex_trylock (tagged_lutex_t tagged_lutex)
+{
+    int ret = 0;
+    struct lutex *lutex = (struct lutex*) native_pointer(tagged_lutex);
+    mach_timespec_t time = {0, 0};
+
+    ret = semaphore_timedwait(lutex->semaphore, time);
+    if (KERN_OPERATION_TIMED_OUT == ret) return ret;
+    lutex_assert(!ret);
+
+    return ret;
+}
+
+int
+lutex_unlock (tagged_lutex_t tagged_lutex)
+{
+    int ret = 0;
+    struct lutex *lutex = (struct lutex*) native_pointer(tagged_lutex);
+
+    ret = semaphore_signal(lutex->semaphore);
+    lutex_assert_verbose(!ret, "ret: %d sem: %lx\n", ret, lutex->semaphore);
+
+    return ret;
+}
+int
+lutex_destroy (tagged_lutex_t tagged_lutex)
+{
+    struct lutex *lutex = (struct lutex*) native_pointer(tagged_lutex);
+    task_t self = mach_task_self();
+    int ret;
+
+    unsigned semaphore = lutex->semaphore;
+
+    if (semaphore) {
+        ret = semaphore_destroy(self, semaphore);
+        lutex->semaphore = 0;
+        if (ret != KERN_SEMAPHORE_DESTROYED)
+            lutex_assert(!ret);
+    }
+
+    return 0;
+}
+#endif
diff --git a/src/runtime/mach-lutex.h b/src/runtime/mach-lutex.h
new file mode 100644
index 0000000..bf69526
--- /dev/null
+++ b/src/runtime/mach-lutex.h
@@ -0,0 +1,24 @@
+/*
+ * This software is part of the SBCL system. See the README file for
+ * more information.
+ *
+ * This software is derived from the CMU CL system, which was
+ * written at Carnegie Mellon University and released into the
+ * public domain. The software is in the public domain and is
+ * provided with absolutely no warranty. See the COPYING and CREDITS
+ * files for more information.
+ */
+
+#ifndef __MACH_LUTEX_H__
+#define __MACH_LUTEX_H__
+
+#if defined(LISP_FEATURE_SB_THREAD) && defined(LISP_FEATURE_SB_MACH_LUTEX)  && defined(LISP_FEATURE_SB_MACH_LUTEX)
+
+typedef unsigned long tagged_lutex_t;
+
+extern int lutex_init (tagged_lutex_t tagged_lutex);
+extern int lutex_destroy (tagged_lutex_t tagged_lutex);
+
+#endif
+
+#endif /* __MACH_LUTEX_H__ */
diff --git a/src/runtime/pthread-lutex.c b/src/runtime/pthread-lutex.c
index 6365214..80723fe 100644
--- a/src/runtime/pthread-lutex.c
+++ b/src/runtime/pthread-lutex.c
@@ -13,7 +13,7 @@
 
 #include "sbcl.h"
 
-#if defined(LISP_FEATURE_SB_THREAD) && defined(LISP_FEATURE_SB_LUTEX)
+#if defined(LISP_FEATURE_SB_THREAD) && defined(LISP_FEATURE_SB_LUTEX)  && !defined(LISP_FEATURE_SB_MACH_LUTEX)
 
 #include <errno.h>
 #include <stdlib.h>
diff --git a/src/runtime/pthread-lutex.h b/src/runtime/pthread-lutex.h
index 69f27c0..86bb240 100644
--- a/src/runtime/pthread-lutex.h
+++ b/src/runtime/pthread-lutex.h
@@ -12,7 +12,7 @@
 #ifndef __PTHREAD_LUTEX_H__
 #define __PTHREAD_LUTEX_H__
 
-#if defined(LISP_FEATURE_SB_THREAD) && defined(LISP_FEATURE_SB_LUTEX)
+#if defined(LISP_FEATURE_SB_THREAD) && defined(LISP_FEATURE_SB_LUTEX) && !defined(LISP_FEATURE_SB_MACH_LUTEX)
 
 typedef unsigned long tagged_lutex_t;