diff --git a/configure.ac b/configure.ac
index 76cb6700..02d4f536 100644
--- a/configure.ac
+++ b/configure.ac
@@ -877,39 +877,32 @@ if test "x${abi}" = "xmacho" ; then
   dnl releases.  malloc_zone_t and malloc_introspection_t have new fields in
   dnl 10.6, which is the only source-level indication of the change.
   AC_MSG_CHECKING([malloc zone version])
-  AC_TRY_COMPILE([#include <stdlib.h>
-#include <malloc/malloc.h>], [
-	static malloc_zone_t zone;
-	static struct malloc_introspection_t zone_introspect;
+  AC_DEFUN([JE_ZONE_PROGRAM],
+    [AC_LANG_PROGRAM(
+      [#include <malloc/malloc.h>],
+      [static foo[[sizeof($1) $2 sizeof(void *) * $3 ? 1 : -1]]]
+    )])
 
-	zone.size = NULL;
-	zone.malloc = NULL;
-	zone.calloc = NULL;
-	zone.valloc = NULL;
-	zone.free = NULL;
-	zone.realloc = NULL;
-	zone.destroy = NULL;
-	zone.zone_name = "jemalloc_zone";
-	zone.batch_malloc = NULL;
-	zone.batch_free = NULL;
-	zone.introspect = &zone_introspect;
-	zone.version = 6;
-	zone.memalign = NULL;
-	zone.free_definite_size = NULL;
-
-	zone_introspect.enumerator = NULL;
-	zone_introspect.good_size = NULL;
-	zone_introspect.check = NULL;
-	zone_introspect.print = NULL;
-	zone_introspect.log = NULL;
-	zone_introspect.force_lock = NULL;
-	zone_introspect.force_unlock = NULL;
-	zone_introspect.statistics = NULL;
-	zone_introspect.zone_locked = NULL;
-], [AC_DEFINE_UNQUOTED([JEMALLOC_ZONE_VERSION], [6])
-    AC_MSG_RESULT([6])],
-   [AC_DEFINE_UNQUOTED([JEMALLOC_ZONE_VERSION], [3])
-   AC_MSG_RESULT([3])])
+  AC_COMPILE_IFELSE([JE_ZONE_PROGRAM(malloc_zone_t,==,14)],[JEMALLOC_ZONE_VERSION=3],[
+  AC_COMPILE_IFELSE([JE_ZONE_PROGRAM(malloc_zone_t,==,15)],[JEMALLOC_ZONE_VERSION=5],[
+  AC_COMPILE_IFELSE([JE_ZONE_PROGRAM(malloc_zone_t,==,16)],[
+    AC_COMPILE_IFELSE([JE_ZONE_PROGRAM(malloc_introspection_t,==,9)],[JEMALLOC_ZONE_VERSION=6],[
+    AC_COMPILE_IFELSE([JE_ZONE_PROGRAM(malloc_introspection_t,==,13)],[JEMALLOC_ZONE_VERSION=7],[JEMALLOC_ZONE_VERSION=]
+  )])],[
+  AC_COMPILE_IFELSE([JE_ZONE_PROGRAM(malloc_zone_t,==,17)],[JEMALLOC_ZONE_VERSION=8],[
+  AC_COMPILE_IFELSE([JE_ZONE_PROGRAM(malloc_zone_t,>,17)],[JEMALLOC_ZONE_VERSION=9],[JEMALLOC_ZONE_VERSION=]
+  )])])])])
+  if test "x${JEMALLOC_ZONE_VERSION}" = "x"; then
+    AC_MSG_RESULT([unsupported])
+    AC_MSG_ERROR([Unsupported malloc zone version])
+  fi
+  if test "${JEMALLOC_ZONE_VERSION}" = 9; then
+    JEMALLOC_ZONE_VERSION=8
+    AC_MSG_RESULT([> 8])
+  else
+    AC_MSG_RESULT([$JEMALLOC_ZONE_VERSION])
+  fi
+  AC_DEFINE_UNQUOTED(JEMALLOC_ZONE_VERSION, [$JEMALLOC_ZONE_VERSION])
 fi
 
 dnl ============================================================================
diff --git a/src/jemalloc.c b/src/jemalloc.c
index e2b61343..2610452e 100644
--- a/src/jemalloc.c
+++ b/src/jemalloc.c
@@ -747,15 +747,23 @@ malloc_init_hard(void)
 	arenas[0] = init_arenas[0];
 
 #ifdef JEMALLOC_ZONE
-	/* Register the custom zone. */
-	malloc_zone_register(create_zone());
+	/* Register the custom zone. At this point it won't be the default. */
+	malloc_zone_t *jemalloc_zone = create_zone();
+	malloc_zone_register(jemalloc_zone);
 
 	/*
-	 * Convert the default szone to an "overlay zone" that is capable of
-	 * deallocating szone-allocated objects, but allocating new objects
-	 * from jemalloc.
+	 * Unregister and reregister the default zone. On OSX >= 10.6,
+	 * unregistering takes the last registered zone and places it at the
+	 * location of the specified zone. Unregistering the default zone thus
+	 * makes the last registered one the default. On OSX < 10.6,
+	 * unregistering shifts all registered zones. The first registered zone
+	 * then becomes the default.
 	 */
-	szone2ozone(malloc_default_zone());
+	do {
+		malloc_zone_t *default_zone = malloc_default_zone();
+		malloc_zone_unregister(default_zone);
+		malloc_zone_register(default_zone);
+	} while (malloc_default_zone() != jemalloc_zone);
 #endif
 
 	malloc_initialized = true;
diff --git a/src/zone.c b/src/zone.c
index a0372e1a..a8f09c98 100644
--- a/src/zone.c
+++ b/src/zone.c
@@ -6,8 +6,8 @@
 /******************************************************************************/
 /* Data. */
 
-static malloc_zone_t zone, szone;
-static struct malloc_introspection_t zone_introspect, ozone_introspect;
+static malloc_zone_t zone;
+static struct malloc_introspection_t zone_introspect;
 
 /******************************************************************************/
 /* Function prototypes for non-inline static functions. */
@@ -18,8 +18,10 @@ static void	*zone_calloc(malloc_zone_t *zone, size_t num, size_t size);
 static void	*zone_valloc(malloc_zone_t *zone, size_t size);
 static void	zone_free(malloc_zone_t *zone, void *ptr);
 static void	*zone_realloc(malloc_zone_t *zone, void *ptr, size_t size);
-#if (JEMALLOC_ZONE_VERSION >= 6)
+#if (JEMALLOC_ZONE_VERSION >= 5)
 static void	*zone_memalign(malloc_zone_t *zone, size_t alignment,
+#endif
+#if (JEMALLOC_ZONE_VERSION >= 6)
     size_t size);
 static void	zone_free_definite_size(malloc_zone_t *zone, void *ptr,
     size_t size);
@@ -28,19 +30,6 @@ static void	*zone_destroy(malloc_zone_t *zone);
 static size_t	zone_good_size(malloc_zone_t *zone, size_t size);
 static void	zone_force_lock(malloc_zone_t *zone);
 static void	zone_force_unlock(malloc_zone_t *zone);
-static size_t	ozone_size(malloc_zone_t *zone, void *ptr);
-static void	ozone_free(malloc_zone_t *zone, void *ptr);
-static void	*ozone_realloc(malloc_zone_t *zone, void *ptr, size_t size);
-static unsigned	ozone_batch_malloc(malloc_zone_t *zone, size_t size,
-    void **results, unsigned num_requested);
-static void	ozone_batch_free(malloc_zone_t *zone, void **to_be_freed,
-    unsigned num);
-#if (JEMALLOC_ZONE_VERSION >= 6)
-static void	ozone_free_definite_size(malloc_zone_t *zone, void *ptr,
-    size_t size);
-#endif
-static void	ozone_force_lock(malloc_zone_t *zone);
-static void	ozone_force_unlock(malloc_zone_t *zone);
 
 /******************************************************************************/
 /*
@@ -101,7 +90,7 @@ zone_realloc(malloc_zone_t *zone, void *ptr, size_t size)
 	return (je_realloc(ptr, size));
 }
 
-#if (JEMALLOC_ZONE_VERSION >= 6)
+#if (JEMALLOC_ZONE_VERSION >= 5)
 static void *
 zone_memalign(malloc_zone_t *zone, size_t alignment, size_t size)
 {
@@ -111,7 +100,9 @@ zone_memalign(malloc_zone_t *zone, size_t alignment, size_t size)
 
 	return (ret);
 }
+#endif
 
+#if (JEMALLOC_ZONE_VERSION >= 6)
 static void
 zone_free_definite_size(malloc_zone_t *zone, void *ptr, size_t size)
 {
@@ -171,10 +162,15 @@ create_zone(void)
 	zone.batch_free = NULL;
 	zone.introspect = &zone_introspect;
 	zone.version = JEMALLOC_ZONE_VERSION;
-#if (JEMALLOC_ZONE_VERSION >= 6)
+#if (JEMALLOC_ZONE_VERSION >= 5)
 	zone.memalign = zone_memalign;
+#endif
+#if (JEMALLOC_ZONE_VERSION >= 6)
 	zone.free_definite_size = zone_free_definite_size;
 #endif
+#if (JEMALLOC_ZONE_VERSION >= 8)
+	zone.pressure_relief = NULL;
+#endif
 
 	zone_introspect.enumerator = NULL;
 	zone_introspect.good_size = (void *)zone_good_size;
@@ -187,156 +183,15 @@ create_zone(void)
 #if (JEMALLOC_ZONE_VERSION >= 6)
 	zone_introspect.zone_locked = NULL;
 #endif
-
+#if (JEMALLOC_ZONE_VERSION >= 7)
+	zone_introspect.enable_discharge_checking = NULL;
+	zone_introspect.disable_discharge_checking = NULL;
+	zone_introspect.discharge = NULL;
+#ifdef __BLOCKS__
+	zone_introspect.enumerate_discharged_pointers = NULL;
+#else
+	zone_introspect.enumerate_unavailable_without_blocks = NULL;
+#endif
+#endif
 	return (&zone);
 }
-
-static size_t
-ozone_size(malloc_zone_t *zone, void *ptr)
-{
-	size_t ret;
-
-	ret = ivsalloc(ptr);
-	if (ret == 0)
-		ret = szone.size(zone, ptr);
-
-	return (ret);
-}
-
-static void
-ozone_free(malloc_zone_t *zone, void *ptr)
-{
-
-	if (ivsalloc(ptr) != 0)
-		je_free(ptr);
-	else {
-		size_t size = szone.size(zone, ptr);
-		if (size != 0)
-			(szone.free)(zone, ptr);
-	}
-}
-
-static void *
-ozone_realloc(malloc_zone_t *zone, void *ptr, size_t size)
-{
-	size_t oldsize;
-
-	if (ptr == NULL)
-		return (je_malloc(size));
-
-	oldsize = ivsalloc(ptr);
-	if (oldsize != 0)
-		return (je_realloc(ptr, size));
-	else {
-		oldsize = szone.size(zone, ptr);
-		if (oldsize == 0)
-			return (je_malloc(size));
-		else {
-			void *ret = je_malloc(size);
-			if (ret != NULL) {
-				memcpy(ret, ptr, (oldsize < size) ? oldsize :
-				    size);
-				(szone.free)(zone, ptr);
-			}
-			return (ret);
-		}
-	}
-}
-
-static unsigned
-ozone_batch_malloc(malloc_zone_t *zone, size_t size, void **results,
-    unsigned num_requested)
-{
-
-	/* Don't bother implementing this interface, since it isn't required. */
-	return (0);
-}
-
-static void
-ozone_batch_free(malloc_zone_t *zone, void **to_be_freed, unsigned num)
-{
-	unsigned i;
-
-	for (i = 0; i < num; i++)
-		ozone_free(zone, to_be_freed[i]);
-}
-
-#if (JEMALLOC_ZONE_VERSION >= 6)
-static void
-ozone_free_definite_size(malloc_zone_t *zone, void *ptr, size_t size)
-{
-
-	if (ivsalloc(ptr) != 0) {
-		assert(ivsalloc(ptr) == size);
-		je_free(ptr);
-	} else {
-		assert(size == szone.size(zone, ptr));
-		szone.free_definite_size(zone, ptr, size);
-	}
-}
-#endif
-
-static void
-ozone_force_lock(malloc_zone_t *zone)
-{
-
-	/* jemalloc locking is taken care of by the normal jemalloc zone. */
-	szone.introspect->force_lock(zone);
-}
-
-static void
-ozone_force_unlock(malloc_zone_t *zone)
-{
-
-	/* jemalloc locking is taken care of by the normal jemalloc zone. */
-	szone.introspect->force_unlock(zone);
-}
-
-/*
- * Overlay the default scalable zone (szone) such that existing allocations are
- * drained, and further allocations come from jemalloc.  This is necessary
- * because Core Foundation directly accesses and uses the szone before the
- * jemalloc library is even loaded.
- */
-void
-szone2ozone(malloc_zone_t *zone)
-{
-
-	/*
-	 * Stash a copy of the original szone so that we can call its
-	 * functions as needed.  Note that the internally, the szone stores its
-	 * bookkeeping data structures immediately following the malloc_zone_t
-	 * header, so when calling szone functions, we need to pass a pointer
-	 * to the original zone structure.
-	 */
-	memcpy(&szone, zone, sizeof(malloc_zone_t));
-
-	zone->size = (void *)ozone_size;
-	zone->malloc = (void *)zone_malloc;
-	zone->calloc = (void *)zone_calloc;
-	zone->valloc = (void *)zone_valloc;
-	zone->free = (void *)ozone_free;
-	zone->realloc = (void *)ozone_realloc;
-	zone->destroy = (void *)zone_destroy;
-	zone->zone_name = "jemalloc_ozone";
-	zone->batch_malloc = ozone_batch_malloc;
-	zone->batch_free = ozone_batch_free;
-	zone->introspect = &ozone_introspect;
-	zone->version = JEMALLOC_ZONE_VERSION;
-#if (JEMALLOC_ZONE_VERSION >= 6)
-	zone->memalign = zone_memalign;
-	zone->free_definite_size = ozone_free_definite_size;
-#endif
-
-	ozone_introspect.enumerator = NULL;
-	ozone_introspect.good_size = (void *)zone_good_size;
-	ozone_introspect.check = NULL;
-	ozone_introspect.print = NULL;
-	ozone_introspect.log = NULL;
-	ozone_introspect.force_lock = (void *)ozone_force_lock;
-	ozone_introspect.force_unlock = (void *)ozone_force_unlock;
-	ozone_introspect.statistics = NULL;
-#if (JEMALLOC_ZONE_VERSION >= 6)
-	ozone_introspect.zone_locked = NULL;
-#endif
-}