diff --git a/c_gen/c_code_gen.py b/c_gen/c_code_gen.py
index 6be7491..df9d9da 100644
--- a/c_gen/c_code_gen.py
+++ b/c_gen/c_code_gen.py
@@ -681,11 +681,12 @@
  *
  * Get length of preceding match object and add to fixed length
  * Applies only to version 1.2 and 1.3
+ * The +2 comes from the 2 bytes of padding between the match and packet data.
  */
 
 #define _PACKET_IN_DATA_OFFSET(obj) \\
-    _OFFSET_FOLLOWING_MATCH_V3((obj), (obj)->version == OF_VERSION_1_2 ? \
-%(packet_in)d : %(packet_in_1_3)d)
+    (_OFFSET_FOLLOWING_MATCH_V3((obj), (obj)->version == OF_VERSION_1_2 ? \
+%(packet_in)d : %(packet_in_1_3)d) + 2)
 
 /**
  * Macro to calculate variable offset of data (packet) member in packet_out
@@ -801,6 +802,7 @@
     common_top_matter(out, name)
     c_type_maps.gen_type_maps(out)
     c_type_maps.gen_length_array(out)
+    c_type_maps.gen_extra_length_array(out)
 
 ################################################################
 # Top Matter
@@ -2642,7 +2644,7 @@
         MEMSET(obj, 0, sizeof(*obj));
     }
     if (bytes < 0) {
-        bytes = of_object_fixed_len[version][%(enum)s];
+        bytes = of_object_fixed_len[version][%(enum)s] + of_object_extra_len[version][%(enum)s];
     }
     obj->version = version;
     obj->length = bytes;
@@ -2789,7 +2791,7 @@
     %(cls)s_t *obj;
     int bytes;
 
-    bytes = of_object_fixed_len[version][%(enum)s];
+    bytes = of_object_fixed_len[version][%(enum)s] + of_object_extra_len[version][%(enum)s];
 
     /* Allocate a maximum-length wire buffer assuming we'll be appending to it. */
     if ((obj = (%(cls)s_t *)of_object_new(OF_WIRE_BUFFER_MAX_LENGTH)) == NULL) {
diff --git a/c_gen/c_test_gen.py b/c_gen/c_test_gen.py
index 74aef8a..54d18b7 100644
--- a/c_gen/c_test_gen.py
+++ b/c_gen/c_test_gen.py
@@ -512,7 +512,7 @@
     """
 
     members, member_types = scalar_member_types_get(cls, version)
-    length = of_g.base_length[(cls, version)]
+    length = of_g.base_length[(cls, version)] + of_g.extra_length.get((cls, version), 0)
     v_name = loxi_utils.version_to_name(version)
 
     out.write("""
@@ -1079,7 +1079,7 @@
         for cls in of_g.ordered_messages:
             if not (cls, version) in of_g.base_length:
                 continue
-            bytes = of_g.base_length[(cls, version)]
+            bytes = of_g.base_length[(cls, version)] + of_g.extra_length.get((cls, version), 0)
             out.write("""
 static int
 test_%(cls)s_create_%(v_name)s(void)
@@ -1488,7 +1488,7 @@
     """
 
     members, member_types = scalar_member_types_get(cls, version)
-    length = of_g.base_length[(cls, version)]
+    length = of_g.base_length[(cls, version)] + of_g.extra_length.get((cls, version), 0)
     v_name = loxi_utils.version_to_name(version)
 
     out.write("""
diff --git a/c_gen/c_type_maps.py b/c_gen/c_type_maps.py
index 07f8dd5..a0fec7e 100644
--- a/c_gen/c_type_maps.py
+++ b/c_gen/c_type_maps.py
@@ -792,6 +792,7 @@
     gen_obj_to_type_map_functions(out)
 
     out.write("extern const int *const of_object_fixed_len[OF_VERSION_ARRAY_MAX];\n")
+    out.write("extern const int *const of_object_extra_len[OF_VERSION_ARRAY_MAX];\n")
 
     out.write("""
 /**
@@ -1064,6 +1065,47 @@
 """)
 
 
+def gen_extra_length_array(out):
+    """
+    Generate an array giving the extra lengths of all objects/versions
+    @param out The file handle to which to write
+    """
+    out.write("""
+/**
+ * An array with the number of bytes in the extra length part
+ * of each OF object
+ */
+""")
+
+    for version in of_g.of_version_range:
+        out.write("""
+static const int\nof_object_extra_len_v%d[OF_OBJECT_COUNT] = {
+    -1,   /* of_object is not instantiable */
+""" % version)
+        for i, cls in enumerate(of_g.all_class_order):
+            comma = ","
+            if i == len(of_g.all_class_order) - 1:
+                comma = ""
+            val = "-1" + comma
+            if (cls, version) in of_g.base_length:
+                val = str(of_g.extra_length.get((cls, version), 0)) + comma
+            out.write("    %-5s /* %d: %s */\n" % (val, i + 1, cls))
+        out.write("};\n")
+
+    out.write("""
+/**
+ * Unified map of extra length part of each object
+ */
+const int *const of_object_extra_len[OF_VERSION_ARRAY_MAX] = {
+    NULL,
+""")
+    for version in of_g.of_version_range:
+        out.write("    of_object_extra_len_v%d,\n" % version)
+    out.write("""
+};
+""")
+
+
 ################################################################
 ################################################################
 
diff --git a/of_g.py b/of_g.py
index bc9888f..2e8b5ba 100644
--- a/of_g.py
+++ b/of_g.py
@@ -406,6 +406,12 @@
 ## Map from class, wire_version to size of fixed part of class
 base_length = {}
 
+## Map from class, wire_version to size of variable-offset, fixed length part of class
+extra_length = {
+    ("of_packet_in", 3): 2,
+    ("of_packet_in", 4): 2,
+}
+
 ## Boolean indication of variable length, per class, wire_version,
 is_fixed_length = set()