diff --git a/src/msgpack/type/bool.hpp b/src/msgpack/type/bool.hpp
index c689f643..06dd3477 100644
--- a/src/msgpack/type/bool.hpp
+++ b/src/msgpack/type/bool.hpp
@@ -24,7 +24,7 @@
 namespace msgpack {
 
 
-inline bool& operator>> (object o, bool& v)
+inline bool& operator>> (object const& o, bool& v)
 {
 	if(o.type != type::BOOLEAN) { throw type_error(); }
 	v = o.via.boolean;
diff --git a/src/msgpack/type/deque.hpp b/src/msgpack/type/deque.hpp
index 878f5d5b..a7c57b03 100644
--- a/src/msgpack/type/deque.hpp
+++ b/src/msgpack/type/deque.hpp
@@ -25,7 +25,7 @@ namespace msgpack {
 
 
 template <typename T>
-inline std::deque<T>& operator>> (object o, std::deque<T>& v)
+inline std::deque<T>& operator>> (object const& o, std::deque<T>& v)
 {
 	if(o.type != type::ARRAY) { throw type_error(); }
 	v.resize(o.via.array.size);
diff --git a/src/msgpack/type/fixint.hpp b/src/msgpack/type/fixint.hpp
index 4f0289da..e68a83ad 100644
--- a/src/msgpack/type/fixint.hpp
+++ b/src/msgpack/type/fixint.hpp
@@ -54,29 +54,29 @@ typedef fix_int<int64_t> fix_int64;
 }  // namespace type
 
 
-inline type::fix_int8& operator>> (object o, type::fix_int8& v)
+inline type::fix_int8& operator>> (object const& o, type::fix_int8& v)
 	{ v = type::detail::convert_integer<int8_t>(o); return v; }
 
-inline type::fix_int16& operator>> (object o, type::fix_int16& v)
+inline type::fix_int16& operator>> (object const& o, type::fix_int16& v)
 	{ v = type::detail::convert_integer<int16_t>(o); return v; }
 
-inline type::fix_int32& operator>> (object o, type::fix_int32& v)
+inline type::fix_int32& operator>> (object const& o, type::fix_int32& v)
 	{ v = type::detail::convert_integer<int32_t>(o); return v; }
 
-inline type::fix_int64& operator>> (object o, type::fix_int64& v)
+inline type::fix_int64& operator>> (object const& o, type::fix_int64& v)
 	{ v = type::detail::convert_integer<int64_t>(o); return v; }
 
 
-inline type::fix_uint8& operator>> (object o, type::fix_uint8& v)
+inline type::fix_uint8& operator>> (object const& o, type::fix_uint8& v)
 	{ v = type::detail::convert_integer<uint8_t>(o); return v; }
 
-inline type::fix_uint16& operator>> (object o, type::fix_uint16& v)
+inline type::fix_uint16& operator>> (object const& o, type::fix_uint16& v)
 	{ v = type::detail::convert_integer<uint16_t>(o); return v; }
 
-inline type::fix_uint32& operator>> (object o, type::fix_uint32& v)
+inline type::fix_uint32& operator>> (object const& o, type::fix_uint32& v)
 	{ v = type::detail::convert_integer<uint32_t>(o); return v; }
 
-inline type::fix_uint64& operator>> (object o, type::fix_uint64& v)
+inline type::fix_uint64& operator>> (object const& o, type::fix_uint64& v)
 	{ v = type::detail::convert_integer<uint64_t>(o); return v; }
 
 
diff --git a/src/msgpack/type/float.hpp b/src/msgpack/type/float.hpp
index 823757cd..fbbe8aed 100644
--- a/src/msgpack/type/float.hpp
+++ b/src/msgpack/type/float.hpp
@@ -27,7 +27,7 @@ namespace msgpack {
 // FIXME check overflow, underflow
 
 
-inline float& operator>> (object o, float& v)
+inline float& operator>> (object const& o, float& v)
 {
 	if(o.type == type::DOUBLE) {
 		v = (float)o.via.dec;
@@ -52,7 +52,7 @@ inline packer<Stream>& operator<< (packer<Stream>& o, const float& v)
 }
 
 
-inline double& operator>> (object o, double& v)
+inline double& operator>> (object const& o, double& v)
 {
 	if(o.type == type::DOUBLE) {
 		v = o.via.dec;
diff --git a/src/msgpack/type/int.hpp b/src/msgpack/type/int.hpp
index 5286f010..5fa638fd 100644
--- a/src/msgpack/type/int.hpp
+++ b/src/msgpack/type/int.hpp
@@ -31,7 +31,7 @@ namespace detail {
 
 	template <typename T>
 	struct convert_integer_sign<T, true> {
-		static inline T convert(object o) {
+		static inline T convert(object const& o) {
 			if(o.type == type::POSITIVE_INTEGER) {
 				if(o.via.u64 > (uint64_t)std::numeric_limits<T>::max())
 					{ throw type_error(); }
@@ -47,7 +47,7 @@ namespace detail {
 
 	template <typename T>
 	struct convert_integer_sign<T, false> {
-		static inline T convert(object o) {
+		static inline T convert(object const& o) {
 			if(o.type == type::POSITIVE_INTEGER) {
 				if(o.via.u64 > (uint64_t)std::numeric_limits<T>::max())
 					{ throw type_error(); }
@@ -121,35 +121,35 @@ inline char& operator>> (object const& o, char& v)
 	{ v = type::detail::convert_integer<char>(o); return v; }
 
 
-inline signed char& operator>> (object o, signed char& v)
+inline signed char& operator>> (object const& o, signed char& v)
 	{ v = type::detail::convert_integer<signed char>(o); return v; }
 
-inline signed short& operator>> (object o, signed short& v)
+inline signed short& operator>> (object const& o, signed short& v)
 	{ v = type::detail::convert_integer<signed short>(o); return v; }
 
-inline signed int& operator>> (object o, signed int& v)
+inline signed int& operator>> (object const& o, signed int& v)
 	{ v = type::detail::convert_integer<signed int>(o); return v; }
 
-inline signed long& operator>> (object o, signed long& v)
+inline signed long& operator>> (object const& o, signed long& v)
 	{ v = type::detail::convert_integer<signed long>(o); return v; }
 
-inline signed long long& operator>> (object o, signed long long& v)
+inline signed long long& operator>> (object const& o, signed long long& v)
 	{ v = type::detail::convert_integer<signed long long>(o); return v; }
 
 
-inline unsigned char& operator>> (object o, unsigned char& v)
+inline unsigned char& operator>> (object const& o, unsigned char& v)
 	{ v = type::detail::convert_integer<unsigned char>(o); return v; }
 
-inline unsigned short& operator>> (object o, unsigned short& v)
+inline unsigned short& operator>> (object const& o, unsigned short& v)
 	{ v = type::detail::convert_integer<unsigned short>(o); return v; }
 
-inline unsigned int& operator>> (object o, unsigned int& v)
+inline unsigned int& operator>> (object const& o, unsigned int& v)
 	{ v = type::detail::convert_integer<unsigned int>(o); return v; }
 
-inline unsigned long& operator>> (object o, unsigned long& v)
+inline unsigned long& operator>> (object const& o, unsigned long& v)
 	{ v = type::detail::convert_integer<unsigned long>(o); return v; }
 
-inline unsigned long long& operator>> (object o, unsigned long long& v)
+inline unsigned long long& operator>> (object const& o, unsigned long long& v)
 	{ v = type::detail::convert_integer<unsigned long long>(o); return v; }
 
 template <typename Stream>
diff --git a/src/msgpack/type/list.hpp b/src/msgpack/type/list.hpp
index eacad035..30f78d62 100644
--- a/src/msgpack/type/list.hpp
+++ b/src/msgpack/type/list.hpp
@@ -25,7 +25,7 @@ namespace msgpack {
 
 
 template <typename T>
-inline std::list<T>& operator>> (object o, std::list<T>& v)
+inline std::list<T>& operator>> (object const& o, std::list<T>& v)
 {
 	if(o.type != type::ARRAY) { throw type_error(); }
 	v.resize(o.via.array.size);
diff --git a/src/msgpack/type/map.hpp b/src/msgpack/type/map.hpp
index 84f6237c..39d64a08 100644
--- a/src/msgpack/type/map.hpp
+++ b/src/msgpack/type/map.hpp
@@ -43,7 +43,7 @@ namespace detail {
 
 
 template <typename K, typename V>
-inline type::assoc_vector<K,V>& operator>> (object o, type::assoc_vector<K,V>& v)
+inline type::assoc_vector<K,V>& operator>> (object const& o, type::assoc_vector<K,V>& v)
 {
 	if(o.type != type::MAP) { throw type_error(); }
 	v.resize(o.via.map.size);
@@ -94,7 +94,7 @@ inline void operator<< (object::with_zone& o, const type::assoc_vector<K,V>& v)
 
 
 template <typename K, typename V>
-inline std::map<K, V> operator>> (object o, std::map<K, V>& v)
+inline std::map<K, V> operator>> (object const& o, std::map<K, V>& v)
 {
 	if(o.type != type::MAP) { throw type_error(); }
 	object_kv* p(o.via.map.ptr);
@@ -150,7 +150,7 @@ inline void operator<< (object::with_zone& o, const std::map<K,V>& v)
 
 
 template <typename K, typename V>
-inline std::multimap<K, V> operator>> (object o, std::multimap<K, V>& v)
+inline std::multimap<K, V> operator>> (object const& o, std::multimap<K, V>& v)
 {
 	if(o.type != type::MAP) { throw type_error(); }
 	object_kv* p(o.via.map.ptr);
diff --git a/src/msgpack/type/nil.hpp b/src/msgpack/type/nil.hpp
index 209bd390..03b9945e 100644
--- a/src/msgpack/type/nil.hpp
+++ b/src/msgpack/type/nil.hpp
@@ -29,7 +29,7 @@ struct nil { };
 }  // namespace type
 
 
-inline type::nil& operator>> (object o, type::nil& v)
+inline type::nil& operator>> (object const& o, type::nil& v)
 {
 	if(o.type != type::NIL) { throw type_error(); }
 	return v;
diff --git a/src/msgpack/type/pair.hpp b/src/msgpack/type/pair.hpp
index 87952365..1b9611e4 100644
--- a/src/msgpack/type/pair.hpp
+++ b/src/msgpack/type/pair.hpp
@@ -25,7 +25,7 @@ namespace msgpack {
 
 
 template <typename T1, typename T2>
-inline std::pair<T1, T2>& operator>> (object o, std::pair<T1, T2>& v)
+inline std::pair<T1, T2>& operator>> (object const& o, std::pair<T1, T2>& v)
 {
 	if(o.type != type::ARRAY) { throw type_error(); }
 	if(o.via.array.size != 2) { throw type_error(); }
diff --git a/src/msgpack/type/raw.hpp b/src/msgpack/type/raw.hpp
index 0f296236..efe2d21c 100644
--- a/src/msgpack/type/raw.hpp
+++ b/src/msgpack/type/raw.hpp
@@ -61,7 +61,7 @@ struct raw_ref {
 }  // namespace type
 
 
-inline type::raw_ref& operator>> (object o, type::raw_ref& v)
+inline type::raw_ref& operator>> (object const& o, type::raw_ref& v)
 {
 	if(o.type != type::RAW) { throw type_error(); }
 	v.ptr  = o.via.raw.ptr;
diff --git a/src/msgpack/type/set.hpp b/src/msgpack/type/set.hpp
index 065e69a6..9b862131 100644
--- a/src/msgpack/type/set.hpp
+++ b/src/msgpack/type/set.hpp
@@ -25,7 +25,7 @@ namespace msgpack {
 
 
 template <typename T>
-inline std::set<T>& operator>> (object o, std::set<T>& v)
+inline std::set<T>& operator>> (object const& o, std::set<T>& v)
 {
 	if(o.type != type::ARRAY) { throw type_error(); }
 	object* p = o.via.array.ptr + o.via.array.size;
@@ -71,7 +71,7 @@ inline void operator<< (object::with_zone& o, const std::set<T>& v)
 
 
 template <typename T>
-inline std::multiset<T>& operator>> (object o, std::multiset<T>& v)
+inline std::multiset<T>& operator>> (object const& o, std::multiset<T>& v)
 {
 	if(o.type != type::ARRAY) { throw type_error(); }
 	object* p = o.via.array.ptr + o.via.array.size;
diff --git a/src/msgpack/type/string.hpp b/src/msgpack/type/string.hpp
index e7839472..4dfe35c8 100644
--- a/src/msgpack/type/string.hpp
+++ b/src/msgpack/type/string.hpp
@@ -24,7 +24,7 @@
 namespace msgpack {
 
 
-inline std::string& operator>> (object o, std::string& v)
+inline std::string& operator>> (object const& o, std::string& v)
 {
 	if(o.type != type::RAW) { throw type_error(); }
 	v.assign(o.via.raw.ptr, o.via.raw.size);
diff --git a/src/msgpack/type/vector.hpp b/src/msgpack/type/vector.hpp
index ce1604ec..4cd1597e 100644
--- a/src/msgpack/type/vector.hpp
+++ b/src/msgpack/type/vector.hpp
@@ -25,7 +25,7 @@ namespace msgpack {
 
 
 template <typename T>
-inline std::vector<T>& operator>> (object o, std::vector<T>& v)
+inline std::vector<T>& operator>> (object const& o, std::vector<T>& v)
 {
 	if(o.type != type::ARRAY) { throw type_error(); }
 	v.resize(o.via.array.size);