diff --git a/python/msgpack/_msgpack.pyx b/python/msgpack/_msgpack.pyx
index eb83c854..61ae36b2 100644
--- a/python/msgpack/_msgpack.pyx
+++ b/python/msgpack/_msgpack.pyx
@@ -71,7 +71,7 @@ cdef class Packer(object):
     def __dealloc__(self):
         free(self.pk.buf);
 
-    cdef int __pack(self, object o):
+    cdef int __pack(self, object o) except -1:
         cdef long long llval
         cdef unsigned long long ullval
         cdef long longval
diff --git a/python/test/test_except.py b/python/test/test_except.py
new file mode 100644
index 00000000..574728fb
--- /dev/null
+++ b/python/test/test_except.py
@@ -0,0 +1,14 @@
+#!/usr/bin/env python
+# coding: utf-8
+
+from nose.tools import *
+from msgpack import packs, unpacks
+
+import datetime
+
+def test_raise_on_find_unsupported_value():
+    assert_raises(TypeError, packs, datetime.datetime.now())
+
+if __name__ == '__main__':
+    from nose import main
+    main()