diff --git a/python/msgpack/_msgpack.pyx b/python/msgpack/_msgpack.pyx
index 6a0b1a5a..85d717e6 100644
--- a/python/msgpack/_msgpack.pyx
+++ b/python/msgpack/_msgpack.pyx
@@ -253,9 +253,7 @@ cdef class Unpacker(object):
         template_init(&self.ctx)
         self.ctx.user.use_list = use_list
 
-    def feed(self, next_bytes):
-        if not isinstance(next_bytes, str):
-           raise ValueError, "Argument must be bytes object"
+    def feed(self, bytes next_bytes):
         self.waiting_bytes.append(next_bytes)
 
     cdef append_buffer(self):