diff --git a/zeroconf.py b/zeroconf.py
index 842173e3d..deaeca634 100644
--- a/zeroconf.py
+++ b/zeroconf.py
@@ -396,7 +396,10 @@ def __init__(self, name, type_, class_, ttl, text):
 
     def write(self, out):
         """Used in constructing an outgoing packet"""
-        out.write_string(self.text)
+        if isinstance(self.text, bytes):
+            out.write_string(self.text)
+        else:
+            out.write_string(b'')
 
     def __eq__(self, other):
         """Tests equality on text"""
@@ -416,6 +419,8 @@ class DNSService(DNSRecord):
 
     def __init__(self, name, type, class_, ttl, priority, weight, port, server):
         DNSRecord.__init__(self, name, type, class_, ttl)
+        assert priority is not None
+        assert port is not None
         self.priority = priority
         self.weight = weight
         self.port = port
@@ -637,7 +642,7 @@ def insert_short(self, index, value):
 
     def write_short(self, value):
         """Writes an unsigned short to the packet"""
-        self.pack(b'!H', value)
+        self.pack(b'!H', int(value))
 
     def write_int(self, value):
         """Writes an unsigned integer to the packet"""
@@ -1054,7 +1059,7 @@ class ServiceInfo(object):
 
     """Service information"""
 
-    def __init__(self, type, name, address=None, port=None, weight=0,
+    def __init__(self, type, name, address=None, port=0, weight=0,
                  priority=0, properties=None, server=None):
         """Create a service description.
 
@@ -1068,6 +1073,8 @@ def __init__(self, type, name, address=None, port=None, weight=0,
                     bytes for the text field)
         server: fully qualified name for service host (defaults to name)"""
 
+        assert priority is not None
+        assert port is not None
         if not name.endswith(type):
             raise BadTypeInNameException
         self.type = type
@@ -1167,8 +1174,10 @@ def update_record(self, zc, now, record):
                 if record.name == self.name:
                     self.server = record.server
                     self.port = record.port
+                    assert self.port is not None
                     self.weight = record.weight
                     self.priority = record.priority
+                    assert self.priority is not None
                     # self.address = None
                     self.update_record(zc, now,
                                        zc.cache.get_by_details(self.server, _TYPE_A, _CLASS_IN))
@@ -1435,6 +1444,7 @@ def register_service(self, info, ttl=_DNS_TTL):
         information for that service.  The name of the service may be
         changed if needed to make it unique on the network."""
         self.check_service(info)
+        assert info.address is not None
         self.services[info.name.lower()] = info
         if info.type in self.servicetypes:
             self.servicetypes[info.type] += 1