diff --git a/wireshark_gen/__init__.py b/wireshark_gen/__init__.py
index c2de4a6..316de21 100644
--- a/wireshark_gen/__init__.py
+++ b/wireshark_gen/__init__.py
@@ -31,6 +31,7 @@
 import loxi_front_end
 import of_g
 from loxi_ir import *
+import field_info
 
 templates_dir = os.path.join(os.path.dirname(os.path.realpath(__file__)), 'templates')
 
@@ -42,6 +43,41 @@
                          ofclass_name[3:],
                          member_name)
 
+def get_field_info(version, cls, name, oftype):
+    """
+    Decide on a Wireshark type and base for a given field.
+
+    Returns (type, base)
+    """
+    if oftype.startswith("list"):
+        return "BYTES", "NONE"
+
+    ofproto = of_g.ir[version]
+    enum = ofproto.enum_by_name(oftype)
+
+    if enum:
+        field_type = "UINT32"
+    elif oftype in field_info.oftype_to_wireshark_type:
+        field_type = field_info.oftype_to_wireshark_type[oftype]
+    else:
+        print "WARN missing oftype_to_wireshark_type for", oftype
+        field_type = "BYTES"
+
+    if enum:
+        if enum.is_bitmask:
+            field_base = "HEX"
+        else:
+            field_base = "DEC"
+    elif oftype in field_info.field_to_base:
+        field_base = field_info.field_to_base[name]
+    elif oftype in field_info.oftype_to_base:
+        field_base = field_info.oftype_to_base[oftype]
+    else:
+        print "WARN missing oftype_to_base for", oftype
+        field_base = "NONE"
+
+    return field_type, field_base
+
 def create_fields():
     r = []
     for wire_version, ofproto in of_g.ir.items():
@@ -50,7 +86,8 @@
                 if isinstance(m, OFPadMember):
                     continue
                 fullname = make_field_name(wire_version, ofclass.name, m.name)
-                r.append(DissectorField(fullname, m.name, "UINT8", "DEC"))
+                field_type, field_base = get_field_info(wire_version, ofclass.name, m.name, m.oftype)
+                r.append(DissectorField(fullname, m.name, field_type, field_base))
 
     return r
 
diff --git a/wireshark_gen/field_info.py b/wireshark_gen/field_info.py
new file mode 100644
index 0000000..09011c7
--- /dev/null
+++ b/wireshark_gen/field_info.py
@@ -0,0 +1,87 @@
+# 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.
+
+# Map from LOXI types to Wireshark types
+oftype_to_wireshark_type = {
+    "char": "INT8",
+    "uint8_t": "UINT8",
+    "uint16_t": "UINT16",
+    "uint32_t": "UINT32",
+    "uint64_t": "UINT64",
+    "of_mac_addr_t": "ETHER",
+    "of_ipv4_t": "IPv4",
+    "of_ipv6_t": "IPv6",
+    "of_port_name_t": "STRINGZ",
+    "of_table_name_t": "STRINGZ",
+    "of_desc_str_t": "STRINGZ",
+    "of_serial_num_t": "STRINGZ",
+    "of_octets_t": "BYTES",
+    "of_port_no_t": "UINT32",
+    "of_port_desc_t": "STRINGZ",
+    "of_bsn_vport_t": "BYTES",
+    "of_bsn_vport_q_in_q_t": "BYTES",
+    "of_fm_cmd_t": "UINT16",
+    "of_wc_bmap_t": "UINT64",
+    "of_match_bmap_t": "UINT64",
+    "of_match_t": "BYTES",
+    "of_oxm_t": "BYTES",
+    "of_meter_features_t": "BYTES",
+}
+
+# Map from LOXI type to Wireshark base
+oftype_to_base = {
+    "char": "DEC",
+    "uint8_t": "DEC",
+    "uint16_t": "DEC",
+    "uint32_t": "DEC",
+    "uint64_t": "DEC",
+    "of_mac_addr_t": "NONE",
+    "of_ipv4_t": "NONE",
+    "of_ipv6_t": "NONE",
+    "of_port_name_t": "NONE",
+    "of_table_name_t": "NONE",
+    "of_desc_str_t": "NONE",
+    "of_serial_num_t": "NONE",
+    "of_octets_t": "NONE",
+    "of_port_no_t": "DEC",
+    "of_port_desc_t": "NONE",
+    "of_bsn_vport_t": "NONE",
+    "of_bsn_vport_q_in_q_t": "NONE",
+    "of_fm_cmd_t": "DEC",
+    "of_wc_bmap_t": "HEX",
+    "of_match_bmap_t": "HEX",
+    "of_match_t": "NONE",
+    "of_oxm_t": "NONE",
+    "of_meter_features_t": "NONE",
+}
+
+# Override oftype_to_base for certain field names
+field_to_base = {
+    "eth_type": "HEX",
+    "cookie": "HEX",
+    "datapath_id": "HEX",
+}