diff --git a/python/msgpack/_msgpack.pyx b/python/msgpack/_msgpack.pyx
index 279fdf5c..e1c497b7 100644
--- a/python/msgpack/_msgpack.pyx
+++ b/python/msgpack/_msgpack.pyx
@@ -9,6 +9,8 @@ cdef extern from "Python.h":
     char* PyString_AsString(object o)
     int PyMapping_Check(object o)
     int PySequence_Check(object o)
+    long long PyLong_AsLongLong(object o)
+    unsigned long long PyLong_AsUnsignedLongLong(object o)
 
 cdef extern from "stdlib.h":
     void* malloc(size_t)
@@ -27,17 +29,18 @@ cdef extern from "pack.h":
         msgpack_packer_write callback
 
     void msgpack_packer_init(msgpack_packer* pk, void* data, msgpack_packer_write callback)
-    void msgpack_pack_int(msgpack_packer* pk, int d)
-    void msgpack_pack_nil(msgpack_packer* pk)
-    void msgpack_pack_true(msgpack_packer* pk)
-    void msgpack_pack_false(msgpack_packer* pk)
-    void msgpack_pack_long(msgpack_packer* pk, long d)
-    void msgpack_pack_long_long(msgpack_packer* pk, long long d)
-    void msgpack_pack_double(msgpack_packer* pk, double d)
-    void msgpack_pack_array(msgpack_packer* pk, size_t l)
-    void msgpack_pack_map(msgpack_packer* pk, size_t l)
-    void msgpack_pack_raw(msgpack_packer* pk, size_t l)
-    void msgpack_pack_raw_body(msgpack_packer* pk, char* body, size_t l)
+    int msgpack_pack_int(msgpack_packer* pk, int d)
+    int msgpack_pack_nil(msgpack_packer* pk)
+    int msgpack_pack_true(msgpack_packer* pk)
+    int msgpack_pack_false(msgpack_packer* pk)
+    int msgpack_pack_long(msgpack_packer* pk, long d)
+    int msgpack_pack_long_long(msgpack_packer* pk, long long d)
+    int msgpack_pack_unsigned_long_long(msgpack_packer* pk, unsigned long long d)
+    int msgpack_pack_double(msgpack_packer* pk, double d)
+    int msgpack_pack_array(msgpack_packer* pk, size_t l)
+    int msgpack_pack_map(msgpack_packer* pk, size_t l)
+    int msgpack_pack_raw(msgpack_packer* pk, size_t l)
+    int msgpack_pack_raw_body(msgpack_packer* pk, char* body, size_t l)
 
 
 cdef class Packer(object):
@@ -103,6 +106,7 @@ cdef class Packer(object):
 
     cdef __pack(self, object o):
         cdef long long llval
+        cdef unsigned long long ullval
         cdef long longval
         cdef double fval
         cdef char* rawval 
@@ -114,8 +118,12 @@ cdef class Packer(object):
         elif o is False:
             msgpack_pack_false(&self.pk)
         elif isinstance(o, long):
-            llval = o
-            msgpack_pack_long_long(&self.pk, llval)
+            if o > 0:
+                ullval = PyLong_AsUnsignedLongLong(o)
+                msgpack_pack_unsigned_long_long(&self.pk, ullval)
+            else:
+                llval = PyLong_AsLongLong(o)
+                msgpack_pack_long_long(&self.pk, llval)
         elif isinstance(o, int):
             longval = o
             msgpack_pack_long(&self.pk, longval)
diff --git a/python/test/test_case.py b/python/test/test_case.py
index 3fafd8b6..997027a5 100644
--- a/python/test/test_case.py
+++ b/python/test/test_case.py
@@ -7,7 +7,7 @@ from msgpack import packs, unpacks
 
 def check(length, obj):
     v = packs(obj)
-    assert_equal(len(v), length)
+    assert_equal(len(v), length, "%r length should be %r but get %r" % (obj, length, len(v)))
     assert_equal(unpacks(v), obj)
 
 def test_1():