diff --git a/configure.ac b/configure.ac
index 0d10143c..2713cbc2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1612,6 +1612,20 @@ if test "x${je_cv_builtin_clz}" = "xyes" ; then
   AC_DEFINE([JEMALLOC_HAVE_BUILTIN_CLZ], [ ])
 fi
 
+dnl ============================================================================
+dnl Check for os_unfair_lock operations as provided on Darwin.
+
+JE_COMPILABLE([Darwin os_unfair_lock_*()], [
+#include <os/lock.h>
+], [
+	os_unfair_lock lock = OS_UNFAIR_LOCK_INIT;
+	os_unfair_lock_lock(&lock);
+	os_unfair_lock_unlock(&lock);
+], [je_cv_os_unfair_lock])
+if test "x${je_cv_os_unfair_lock}" = "xyes" ; then
+  AC_DEFINE([JEMALLOC_OS_UNFAIR_LOCK], [ ])
+fi
+
 dnl ============================================================================
 dnl Check for spinlock(3) operations as provided on Darwin.
 
diff --git a/include/jemalloc/internal/jemalloc_internal_decls.h b/include/jemalloc/internal/jemalloc_internal_decls.h
index 1d7f2075..c907d910 100644
--- a/include/jemalloc/internal/jemalloc_internal_decls.h
+++ b/include/jemalloc/internal/jemalloc_internal_decls.h
@@ -17,6 +17,9 @@
 #    include <sys/uio.h>
 #  endif
 #  include <pthread.h>
+#  ifdef JEMALLOC_OS_UNFAIR_LOCK
+#    include <os/lock.h>
+#  endif
 #  ifdef JEMALLOC_GLIBC_MALLOC_HOOK
 #    include <sched.h>
 #  endif
diff --git a/include/jemalloc/internal/jemalloc_internal_defs.h.in b/include/jemalloc/internal/jemalloc_internal_defs.h.in
index 0ba960ba..dcbad728 100644
--- a/include/jemalloc/internal/jemalloc_internal_defs.h.in
+++ b/include/jemalloc/internal/jemalloc_internal_defs.h.in
@@ -60,6 +60,11 @@
  */
 #undef JEMALLOC_HAVE_MADVISE
 
+/*
+ * Defined if os_unfair_lock_*() functions are available, as provided by Darwin.
+ */
+#undef JEMALLOC_OS_UNFAIR_LOCK
+
 /*
  * Defined if OSSpin*() functions are available, as provided by Darwin, and
  * documented in the spinlock(3) manual page.
diff --git a/include/jemalloc/internal/mutex.h b/include/jemalloc/internal/mutex.h
index b4e01ff8..d5b3693c 100644
--- a/include/jemalloc/internal/mutex.h
+++ b/include/jemalloc/internal/mutex.h
@@ -5,6 +5,9 @@ typedef struct malloc_mutex_s malloc_mutex_t;
 
 #ifdef _WIN32
 #  define MALLOC_MUTEX_INITIALIZER
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
+#  define MALLOC_MUTEX_INITIALIZER					\
+     {OS_UNFAIR_LOCK_INIT, WITNESS_INITIALIZER("mutex", WITNESS_RANK_OMIT)}
 #elif (defined(JEMALLOC_OSSPIN))
 #  define MALLOC_MUTEX_INITIALIZER					\
      {0, WITNESS_INITIALIZER("mutex", WITNESS_RANK_OMIT)}
@@ -38,6 +41,8 @@ struct malloc_mutex_s {
 #  else
 	CRITICAL_SECTION	lock;
 #  endif
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
+	os_unfair_lock		lock;
 #elif (defined(JEMALLOC_OSSPIN))
 	OSSpinLock		lock;
 #elif (defined(JEMALLOC_MUTEX_INIT_CB))
@@ -91,6 +96,8 @@ malloc_mutex_lock(tsdn_t *tsdn, malloc_mutex_t *mutex)
 #  else
 		EnterCriticalSection(&mutex->lock);
 #  endif
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
+		os_unfair_lock_lock(&mutex->lock);
 #elif (defined(JEMALLOC_OSSPIN))
 		OSSpinLockLock(&mutex->lock);
 #else
@@ -112,6 +119,8 @@ malloc_mutex_unlock(tsdn_t *tsdn, malloc_mutex_t *mutex)
 #  else
 		LeaveCriticalSection(&mutex->lock);
 #  endif
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
+		os_unfair_lock_unlock(&mutex->lock);
 #elif (defined(JEMALLOC_OSSPIN))
 		OSSpinLockUnlock(&mutex->lock);
 #else
diff --git a/src/mutex.c b/src/mutex.c
index 119b8e35..b757ba86 100644
--- a/src/mutex.c
+++ b/src/mutex.c
@@ -80,6 +80,8 @@ malloc_mutex_init(malloc_mutex_t *mutex, const char *name, witness_rank_t rank)
 	    _CRT_SPINCOUNT))
 		return (true);
 #  endif
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
+	mutex->lock = OS_UNFAIR_LOCK_INIT;
 #elif (defined(JEMALLOC_OSSPIN))
 	mutex->lock = 0;
 #elif (defined(JEMALLOC_MUTEX_INIT_CB))
diff --git a/test/include/test/mtx.h b/test/include/test/mtx.h
index bbe822f5..58afbc3d 100644
--- a/test/include/test/mtx.h
+++ b/test/include/test/mtx.h
@@ -8,6 +8,8 @@
 typedef struct {
 #ifdef _WIN32
 	CRITICAL_SECTION	lock;
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
+	os_unfair_lock		lock;
 #elif (defined(JEMALLOC_OSSPIN))
 	OSSpinLock		lock;
 #else
diff --git a/test/src/mtx.c b/test/src/mtx.c
index 73bd02f6..8a5dfdd9 100644
--- a/test/src/mtx.c
+++ b/test/src/mtx.c
@@ -11,6 +11,8 @@ mtx_init(mtx_t *mtx)
 #ifdef _WIN32
 	if (!InitializeCriticalSectionAndSpinCount(&mtx->lock, _CRT_SPINCOUNT))
 		return (true);
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
+	mtx->lock = OS_UNFAIR_LOCK_INIT;
 #elif (defined(JEMALLOC_OSSPIN))
 	mtx->lock = 0;
 #else
@@ -33,6 +35,7 @@ mtx_fini(mtx_t *mtx)
 {
 
 #ifdef _WIN32
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
 #elif (defined(JEMALLOC_OSSPIN))
 #else
 	pthread_mutex_destroy(&mtx->lock);
@@ -45,6 +48,8 @@ mtx_lock(mtx_t *mtx)
 
 #ifdef _WIN32
 	EnterCriticalSection(&mtx->lock);
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
+	os_unfair_lock_lock(&mtx->lock);
 #elif (defined(JEMALLOC_OSSPIN))
 	OSSpinLockLock(&mtx->lock);
 #else
@@ -58,6 +63,8 @@ mtx_unlock(mtx_t *mtx)
 
 #ifdef _WIN32
 	LeaveCriticalSection(&mtx->lock);
+#elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
+	os_unfair_lock_unlock(&mtx->lock);
 #elif (defined(JEMALLOC_OSSPIN))
 	OSSpinLockUnlock(&mtx->lock);
 #else