diff --git a/coapthon/client/coap.py b/coapthon/client/coap.py
index 5a3747c..0bf3e28 100644
--- a/coapthon/client/coap.py
+++ b/coapthon/client/coap.py
@@ -178,7 +178,7 @@ class CoAP(object):
                 if opt.value == 26:
                     return
 
-        if self._receiver_thread is None or not self._receiver_thread.isAlive():
+        if self._receiver_thread is None or not self._receiver_thread.is_alive():
             self._receiver_thread = threading.Thread(target=self.receive_datagram)
             self._receiver_thread.daemon = True
             self._receiver_thread.start()
diff --git a/coapthon/messages/message.py b/coapthon/messages/message.py
index 98e4a76..e4fd61d 100644
--- a/coapthon/messages/message.py
+++ b/coapthon/messages/message.py
@@ -127,7 +127,7 @@ class Message(object):
             self._token = value
             return
         if not isinstance(value, bytes):
-            value = bytes(value)
+            value = bytes(value, 'utf-8')
 
         if len(value) > 256:
             raise AttributeError
@@ -645,7 +645,8 @@ class Message(object):
         Delete the Block2 option.
         """
         self.del_option_by_number(defines.OptionRegistry.BLOCK2.number)
-        
+
+    @property
     def size1(self):
         value = None
         for option in self.options: