diff --git a/py_gen/codegen.py b/py_gen/codegen.py
index 01dd782..82bf772 100644
--- a/py_gen/codegen.py
+++ b/py_gen/codegen.py
@@ -37,9 +37,18 @@
                                  'min_length', 'is_fixed_length'])
 Member = namedtuple('Member', ['name', 'oftype', 'offset', 'skip'])
 LengthMember = namedtuple('LengthMember', ['name', 'oftype', 'offset'])
+FieldLengthMember = namedtuple('FieldLengthMember', ['name', 'oftype', 'offset', 'field_name'])
 TypeMember = namedtuple('TypeMember', ['name', 'oftype', 'offset', 'value'])
 PadMember = namedtuple('PadMember', ['offset', 'length'])
 
+# XXX move to frontend
+field_length_members = {
+    ('of_packet_out', 1, 'actions_len') : 'actions',
+    ('of_packet_out', 2, 'actions_len') : 'actions',
+    ('of_packet_out', 3, 'actions_len') : 'actions',
+    ('of_packet_out', 4, 'actions_len') : 'actions',
+}
+
 def get_type_values(cls, version):
     """
     Returns a map from the name of the type member to its value.
@@ -112,6 +121,12 @@
                 members.append(LengthMember(name=member['name'],
                                             offset=member['offset'],
                                             oftype=oftype.OFType(member['m_type'], version)))
+            elif (cls, version, member['name']) in field_length_members:
+                field_name = field_length_members[(cls, version, member['name'])]
+                members.append(FieldLengthMember(name=member['name'],
+                                                 offset=member['offset'],
+                                                 oftype=oftype.OFType(member['m_type'], version),
+                                                 field_name=field_name))
             elif member['name'] in type_values:
                 members.append(TypeMember(name=member['name'],
                                           offset=member['offset'],
diff --git a/py_gen/templates/_pack.py b/py_gen/templates/_pack.py
index 66ee763..e853833 100644
--- a/py_gen/templates/_pack.py
+++ b/py_gen/templates/_pack.py
@@ -26,19 +26,30 @@
 :: # under the EPL.
 ::
 :: # TODO coalesce format strings
-:: from py_gen.codegen import Member, LengthMember, TypeMember, PadMember
+:: from py_gen.codegen import Member, LengthMember, FieldLengthMember, TypeMember, PadMember
 :: length_member = None
 :: length_member_index = None
+:: field_length_members = {}
+:: field_length_indexes = {}
 :: index = 0
 :: for m in ofclass.members:
 ::     if type(m) == LengthMember:
 ::         length_member = m
 ::         length_member_index = index
-        packed.append(${m.oftype.gen_pack_expr('0')}) # placeholder for ${m.name} at index ${length_member_index}
+        packed.append(${m.oftype.gen_pack_expr('0')}) # placeholder for ${m.name} at index ${index}
+::     elif type(m) == FieldLengthMember:
+::         field_length_members[m.field_name] = m
+::         field_length_indexes[m.field_name] = index
+        packed.append(${m.oftype.gen_pack_expr('0')}) # placeholder for ${m.name} at index ${index}
 ::     elif type(m) == PadMember:
         packed.append('\x00' * ${m.length})
 ::     else:
         packed.append(${m.oftype.gen_pack_expr('self.' + m.name)})
+::         if m.name in field_length_members:
+::             field_length_member = field_length_members[m.name]
+::             field_length_index = field_length_indexes[m.name]
+        packed[${field_length_index}] = ${field_length_member.oftype.gen_pack_expr('len(packed[-1])')}
+::         #endif
 ::     #endif
 ::     index += 1
 :: #endfor
diff --git a/py_gen/templates/_pack_packet_out.py b/py_gen/templates/_pack_packet_out.py
deleted file mode 100644
index ad8b827..0000000
--- a/py_gen/templates/_pack_packet_out.py
+++ /dev/null
@@ -1,39 +0,0 @@
-:: # Copyright 2013, Big Switch Networks, Inc.
-:: #
-:: # LoxiGen is licensed under the Eclipse Public License, version 1.0 (EPL), with
-:: # the following special exception:
-:: #
-:: # LOXI Exception
-:: #
-:: # As a special exception to the terms of the EPL, you may distribute libraries
-:: # generated by LoxiGen (LoxiGen Libraries) under the terms of your choice, provided
-:: # that copyright and licensing notices generated by LoxiGen are not altered or removed
-:: # from the LoxiGen Libraries and the notice provided below is (i) included in
-:: # the LoxiGen Libraries, if distributed in source code form and (ii) included in any
-:: # documentation for the LoxiGen Libraries, if distributed in binary form.
-:: #
-:: # Notice: "Copyright 2013, Big Switch Networks, Inc. This library was generated by the LoxiGen Compiler."
-:: #
-:: # You may not use this file except in compliance with the EPL or LOXI Exception. You may obtain
-:: # a copy of the EPL at:
-:: #
-:: # http://www.eclipse.org/legal/epl-v10.html
-:: #
-:: # Unless required by applicable law or agreed to in writing, software
-:: # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-:: # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-:: # EPL for the specific language governing permissions and limitations
-:: # under the EPL.
-::
-        packed.append(struct.pack("!B", self.version))
-        packed.append(struct.pack("!B", self.type))
-        packed.append(struct.pack("!H", 0)) # placeholder for length at index 3
-        packed.append(struct.pack("!L", self.xid))
-        packed.append(struct.pack("!L", self.buffer_id))
-        packed.append(struct.pack("!H", self.in_port))
-        packed_actions = "".join([x.pack() for x in self.actions])
-        packed.append(struct.pack("!H", len(packed_actions)))
-        packed.append(packed_actions)
-        packed.append(self.data)
-        length = sum([len(x) for x in packed])
-        packed[2] = struct.pack("!H", length)
diff --git a/py_gen/templates/_unpack.py b/py_gen/templates/_unpack.py
index 8be8254..6bf0db6 100644
--- a/py_gen/templates/_unpack.py
+++ b/py_gen/templates/_unpack.py
@@ -26,23 +26,29 @@
 :: # under the EPL.
 ::
 :: # TODO coalesce format strings
-:: from py_gen.codegen import Member, LengthMember, TypeMember, PadMember
+:: from py_gen.codegen import Member, LengthMember, FieldLengthMember, TypeMember, PadMember
         if type(buf) == loxi.generic_util.OFReader:
             reader = buf
         else:
             reader = loxi.generic_util.OFReader(buf)
+:: field_length_members = {}
 :: for m in ofclass.members:
 ::     if type(m) == PadMember:
         reader.skip(${m.length})
-::         continue
-::     #endif
-::     unpack_expr = m.oftype.gen_unpack_expr('reader')
-::     if type(m) == LengthMember:
-        _${m.name} = ${unpack_expr}
+::     elif type(m) == LengthMember:
+        _${m.name} = ${m.oftype.gen_unpack_expr('reader')}
+::     elif type(m) == FieldLengthMember:
+::         field_length_members[m.field_name] = m
+        _${m.name} = ${m.oftype.gen_unpack_expr('reader')}
 ::     elif type(m) == TypeMember:
-        _${m.name} = ${unpack_expr}
+        _${m.name} = ${m.oftype.gen_unpack_expr('reader')}
         assert(_${m.name} == ${m.value})
-::     else:
-        obj.${m.name} = ${unpack_expr}
+::     elif type(m) == Member:
+::         if m.name in field_length_members:
+::             reader_expr = 'reader.slice(_%s)' % field_length_members[m.name].name
+::         else:
+::             reader_expr = 'reader'
+::         #endif
+        obj.${m.name} = ${m.oftype.gen_unpack_expr(reader_expr)}
 ::     #endif
 :: #endfor
diff --git a/py_gen/templates/_unpack_packet_out.py b/py_gen/templates/_unpack_packet_out.py
deleted file mode 100644
index f7f9683..0000000
--- a/py_gen/templates/_unpack_packet_out.py
+++ /dev/null
@@ -1,42 +0,0 @@
-:: # Copyright 2013, Big Switch Networks, Inc.
-:: #
-:: # LoxiGen is licensed under the Eclipse Public License, version 1.0 (EPL), with
-:: # the following special exception:
-:: #
-:: # LOXI Exception
-:: #
-:: # As a special exception to the terms of the EPL, you may distribute libraries
-:: # generated by LoxiGen (LoxiGen Libraries) under the terms of your choice, provided
-:: # that copyright and licensing notices generated by LoxiGen are not altered or removed
-:: # from the LoxiGen Libraries and the notice provided below is (i) included in
-:: # the LoxiGen Libraries, if distributed in source code form and (ii) included in any
-:: # documentation for the LoxiGen Libraries, if distributed in binary form.
-:: #
-:: # Notice: "Copyright 2013, Big Switch Networks, Inc. This library was generated by the LoxiGen Compiler."
-:: #
-:: # You may not use this file except in compliance with the EPL or LOXI Exception. You may obtain
-:: # a copy of the EPL at:
-:: #
-:: # http://www.eclipse.org/legal/epl-v10.html
-:: #
-:: # Unless required by applicable law or agreed to in writing, software
-:: # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-:: # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-:: # EPL for the specific language governing permissions and limitations
-:: # under the EPL.
-::
-        if type(buf) == loxi.generic_util.OFReader:
-            reader = buf
-        else:
-            reader = loxi.generic_util.OFReader(buf)
-        _version = reader.read('!B')[0]
-        assert(_version == const.OFP_VERSION)
-        _type = reader.read('!B')[0]
-        assert(_type == const.OFPT_PACKET_OUT)
-        _length = reader.read('!H')[0]
-        obj.xid = reader.read('!L')[0]
-        obj.buffer_id = reader.read('!L')[0]
-        obj.in_port = reader.read('!H')[0]
-        _actions_len = reader.read('!H')[0]
-        obj.actions = action.unpack_list(reader.slice(_actions_len))
-        obj.data = str(reader.read_all())
diff --git a/py_gen/templates/message.py b/py_gen/templates/message.py
index d501854..86fb3bf 100644
--- a/py_gen/templates/message.py
+++ b/py_gen/templates/message.py
@@ -64,22 +64,14 @@
 
     def pack(self):
         packed = []
-:: if ofclass.name == 'of_packet_out':
-:: include('_pack_packet_out.py', ofclass=ofclass)
-:: else:
 :: include('_pack.py', ofclass=ofclass)
-:: #endif
         return ''.join(packed)
 
     @staticmethod
     def unpack(buf):
         if len(buf) < 8: raise loxi.ProtocolError("buffer too short to contain an OpenFlow message")
         obj = ${ofclass.pyname}()
-:: if ofclass.name == 'of_packet_out':
-:: include('_unpack_packet_out.py', ofclass=ofclass)
-:: else:
 :: include('_unpack.py', ofclass=ofclass)
-:: #endif
         return obj
 
     def __eq__(self, other):