diff --git a/example/speed_test.cc b/example/speed_test.cc
index 570cb1bf..267c042b 100644
--- a/example/speed_test.cc
+++ b/example/speed_test.cc
@@ -31,7 +31,7 @@ void test_map_pack_unpack() {
 	std::cout << "Start unpacking..." << std::endl;
 	{
 		boost::timer::cpu_timer timer;
-		msgpack::unpack(str.data(), str.size(), NULL, &mempool, deserialized);
+		msgpack::unpack(str.data(), str.size(), NULL, mempool, deserialized);
 		std::string result = timer.format();
 		std::cout << result << std::endl;
 	}
diff --git a/src/msgpack/unpack.hpp b/src/msgpack/unpack.hpp
index dc136800..11bcbd06 100644
--- a/src/msgpack/unpack.hpp
+++ b/src/msgpack/unpack.hpp
@@ -50,8 +50,9 @@ namespace detail {
 
 class unpack_user {
 public:
-	zone* z() const { return z_; }
-	void set_z(zone* z) { z_ = z; }
+	zone const& z() const { return *z_; }
+	zone& z() { return *z_; }
+	void set_z(zone& z) { z_ = &z; }
 	bool referenced() const { return referenced_; }
 	void set_referenced(bool referenced) { referenced_ = referenced; }
 private:
@@ -109,7 +110,7 @@ inline int template_callback_array(unpack_user* u, unsigned int n, object& o)
 {
 	o.type = type::ARRAY;
 	o.via.array.size = 0;
-	o.via.array.ptr = (object*)u->z()->malloc(n*sizeof(object));
+	o.via.array.ptr = (object*)u->z().malloc(n*sizeof(object));
 	if(o.via.array.ptr == NULL) { return -1; }
 	return 0;
 }
@@ -121,7 +122,7 @@ inline int template_callback_map(unpack_user* u, unsigned int n, object& o)
 {
 	o.type = type::MAP;
 	o.via.map.size = 0;
-	o.via.map.ptr = (object_kv*)u->z()->malloc(n*sizeof(object_kv));
+	o.via.map.ptr = (object_kv*)u->z().malloc(n*sizeof(object_kv));
 	if(o.via.map.ptr == NULL) { return -1; }
 	return 0;
 }
@@ -684,7 +685,7 @@ typedef enum {
 
 // obsolete
 static unpack_return unpack(const char* data, size_t len, size_t* off,
-		zone* z, object& result);
+		zone& z, object& result);
 
 
 // obsolete
@@ -719,7 +720,7 @@ inline unpacker::unpacker(size_t initial_buffer_size)
 	detail::init_count(buffer_);
 
 	ctx_.init();
-	ctx_.user().set_z(z_);
+	ctx_.user().set_z(*z_);
 	ctx_.user().set_referenced(false);
 }
 
@@ -876,7 +877,7 @@ inline zone* unpacker::release_zone()
 
 	zone* old = z_;
 	z_ = r;
-	ctx_.user().set_z(z_);
+	ctx_.user().set_z(*z_);
 
 	return old;
 }
@@ -943,7 +944,7 @@ namespace detail {
 
 inline unpack_return
 unpack_imp(const char* data, size_t len, size_t* off,
-		zone* result_zone, object& result)
+		zone& result_zone, object& result)
 {
 	size_t noff = 0;
 	if(off != NULL) { noff = *off; }
@@ -988,7 +989,7 @@ inline void unpack(unpacked* result,
 	msgpack::unique_ptr<zone> z(new zone());
 
 	unpack_return ret = detail::unpack_imp(
-			data, len, offset, z.get(), obj);
+			data, len, offset, *z, obj);
 
 
 	switch(ret) {
@@ -1014,7 +1015,7 @@ inline void unpack(unpacked* result,
 
 // obsolete
 inline unpack_return unpack(const char* data, size_t len, size_t* off,
-		zone* z, object& result)
+		zone& z, object& result)
 {
 	return detail::unpack_imp(data, len, off,
 			z, result);
@@ -1025,7 +1026,7 @@ inline object unpack(const char* data, size_t len, zone& z, size_t* off)
 {
 	object result;
 
-	switch( unpack(data, len, off, &z, result) ) {
+	switch( unpack(data, len, off, z, result) ) {
 	case UNPACK_SUCCESS:
 		return result;
 
diff --git a/test/msgpack_test.cpp b/test/msgpack_test.cpp
index f00637d3..5e23e51c 100644
--- a/test/msgpack_test.cpp
+++ b/test/msgpack_test.cpp
@@ -38,7 +38,7 @@ const double kEPS = 1e-10;
       msgpack::zone z;                                                \
       msgpack::object obj;                                            \
       msgpack::unpack_return ret =                                    \
-        msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);    \
+        msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);    \
       EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);                        \
       test_type val2;                                                 \
       obj.convert(&val2);                                             \
@@ -165,7 +165,7 @@ TEST(MSGPACK, simple_buffer_float)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     float val2;
     obj.convert(&val2);
@@ -255,7 +255,7 @@ TEST(MSGPACK, simple_buffer_double)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     double val2;
     obj.convert(&val2);
@@ -277,7 +277,7 @@ TEST(MSGPACK, simple_buffer_true)
   msgpack::zone z;
   msgpack::object obj;
   msgpack::unpack_return ret =
-    msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+    msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
   EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
   bool val2;
   obj.convert(&val2);
@@ -292,7 +292,7 @@ TEST(MSGPACK, simple_buffer_false)
   msgpack::zone z;
   msgpack::object obj;
   msgpack::unpack_return ret =
-    msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+    msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
   EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
   bool val2;
   obj.convert(&val2);
@@ -314,7 +314,7 @@ TEST(MSGPACK_STL, simple_buffer_string)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     string val2;
     obj.convert(&val2);
@@ -334,7 +334,7 @@ TEST(MSGPACK_STL, simple_buffer_vector)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     vector<int> val2;
     obj.convert(&val2);
@@ -354,7 +354,7 @@ TEST(MSGPACK_STL, simple_buffer_map)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     map<int, int> val2;
     obj.convert(&val2);
@@ -374,7 +374,7 @@ TEST(MSGPACK_STL, simple_buffer_deque)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     deque<int> val2;
     obj.convert(&val2);
@@ -394,7 +394,7 @@ TEST(MSGPACK_STL, simple_buffer_list)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     list<int> val2;
     obj.convert(&val2);
@@ -414,7 +414,7 @@ TEST(MSGPACK_STL, simple_buffer_set)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     set<int> val2;
     obj.convert(&val2);
@@ -432,7 +432,7 @@ TEST(MSGPACK_STL, simple_buffer_pair)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     pair<int, int> val2;
     obj.convert(&val2);
@@ -455,7 +455,7 @@ TEST(MSGPACK_STL, simple_buffer_multimap)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     multimap<int, int> val2;
     obj.convert(&val2);
@@ -485,7 +485,7 @@ TEST(MSGPACK_STL, simple_buffer_multiset)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     multiset<int> val2;
     obj.convert(&val2);
@@ -520,7 +520,7 @@ TEST(MSGPACK_TR1, simple_buffer_tr1_unordered_map)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     tr1::unordered_map<int, int> val2;
     obj.convert(&val2);
@@ -547,7 +547,7 @@ TEST(MSGPACK_TR1, simple_buffer_tr1_unordered_multimap)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     tr1::unordered_multimap<int, int> val2;
     obj.convert(&val2);
@@ -581,7 +581,7 @@ TEST(MSGPACK_TR1, simple_buffer_tr1_unordered_set)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     tr1::unordered_set<int> val2;
     obj.convert(&val2);
@@ -603,7 +603,7 @@ TEST(MSGPACK_TR1, simple_buffer_tr1_unordered_multiset)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     tr1::unordered_multiset<int> val2;
     obj.convert(&val2);
@@ -760,7 +760,7 @@ TEST(MSGPACK_USER_DEFINED, simple_buffer_class)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     TestClass val2;
     val2.i = -1;
@@ -793,7 +793,7 @@ TEST(MSGPACK_USER_DEFINED, simple_buffer_class_old_to_new)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     TestClass2 val2;
     val2.i = -1;
@@ -815,7 +815,7 @@ TEST(MSGPACK_USER_DEFINED, simple_buffer_class_new_to_old)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     TestClass val2;
     val2.i = -1;
@@ -856,7 +856,7 @@ TEST(MSGPACK_USER_DEFINED, simple_buffer_enum_member)
   msgpack::zone z;
   msgpack::object obj;
   msgpack::unpack_return ret =
-    msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+    msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
   EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
   TestEnumMemberClass val2;
   val2.t1 = TestEnumMemberClass::STATE_INVALID;
@@ -919,7 +919,7 @@ TEST(MSGPACK_USER_DEFINED, simple_buffer_union_member)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     TestUnionMemberClass val2;
     obj.convert(&val2);
@@ -934,7 +934,7 @@ TEST(MSGPACK_USER_DEFINED, simple_buffer_union_member)
     msgpack::zone z;
     msgpack::object obj;
     msgpack::unpack_return ret =
-      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+      msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
     EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);
     TestUnionMemberClass val2;
     obj.convert(&val2);
@@ -962,7 +962,7 @@ TEST(MSGPACK_USER_DEFINED, simple_buffer_union_member)
       msgpack::zone z;                                                  \
       msgpack::object obj;                                              \
       msgpack::unpack_return ret =                                      \
-        msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);      \
+        msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);        \
       EXPECT_EQ(msgpack::UNPACK_SUCCESS, ret);                          \
       test_type val2;                                                   \
       obj.convert(&val2);                                               \
diff --git a/test/object.cc b/test/object.cc
index 71c1e59c..7a6b0a87 100644
--- a/test/object.cc
+++ b/test/object.cc
@@ -37,7 +37,7 @@ TEST(object, convert)
 	msgpack::object obj;
 
 	msgpack::unpack_return ret =
-		msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+		msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
 	EXPECT_EQ(ret, msgpack::UNPACK_SUCCESS);
 
 	myclass m2;
@@ -58,7 +58,7 @@ TEST(object, as)
 	msgpack::object obj;
 
 	msgpack::unpack_return ret =
-		msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+		msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
 	EXPECT_EQ(ret, msgpack::UNPACK_SUCCESS);
 
 	EXPECT_EQ(m1, obj.as<myclass>());
diff --git a/test/pack_unpack.cc b/test/pack_unpack.cc
index 19a20baf..6718a01b 100644
--- a/test/pack_unpack.cc
+++ b/test/pack_unpack.cc
@@ -60,7 +60,7 @@ TEST(unpack, myclass)
 	msgpack::object obj;
 
 	msgpack::unpack_return ret =
-		msgpack::unpack(sbuf.data(), sbuf.size(), NULL, &z, obj);
+		msgpack::unpack(sbuf.data(), sbuf.size(), NULL, z, obj);
 
 	EXPECT_EQ(ret, msgpack::UNPACK_SUCCESS);
 
@@ -105,17 +105,17 @@ TEST(unpack, sequence_compat)
 	msgpack::object obj;
 	msgpack::unpack_return ret;
 
-	ret = msgpack::unpack(sbuf.data(), sbuf.size(), &offset, &z, obj);
+	ret = msgpack::unpack(sbuf.data(), sbuf.size(), &offset, z, obj);
 	EXPECT_TRUE(ret >= 0);
 	EXPECT_EQ(ret, msgpack::UNPACK_EXTRA_BYTES);
 	EXPECT_EQ(1, obj.as<int>());
 
-	ret = msgpack::unpack(sbuf.data(), sbuf.size(), &offset, &z, obj);
+	ret = msgpack::unpack(sbuf.data(), sbuf.size(), &offset, z, obj);
 	EXPECT_TRUE(ret >= 0);
 	EXPECT_EQ(ret, msgpack::UNPACK_EXTRA_BYTES);
 	EXPECT_EQ(2, obj.as<int>());
 
-	ret = msgpack::unpack(sbuf.data(), sbuf.size(), &offset, &z, obj);
+	ret = msgpack::unpack(sbuf.data(), sbuf.size(), &offset, z, obj);
 	EXPECT_TRUE(ret >= 0);
 	EXPECT_EQ(ret, msgpack::UNPACK_SUCCESS);
 	EXPECT_EQ(3, obj.as<int>());